Because of their poverty, medieval appearances and customs, unwillingness to change their habits, to learn the Polish language, and to support the newly reborn country they were seen as liability by both the Poles and their own more progressive brethren.
They were so visible to the traveling by car foreign visitors, they frequently asked themselves "where are the Poles?".
And they were the main, and the most helpless victims of the Nazi Germany, and the Stalinist Russia.
This is what Ben-Zion Gold has to say about them in The Life of Jews in Poland Before the Holocaust:
The Polish orthodox Jews a hundred years earlier, as seen by the American writer and traveler, John Stephens, from Incidents of Travel in Greece, Turkey, Russia, and Poland:My father, who was familiar with Polish politics, had com to the conclusion that Jews had no future in Poland. Though he was not formally a Zionist, yearning for Zion was part of his daily life. As a religious Jew he prayed many times in the course of the day for the return to Zion and Jerusalem. Hitler's rise to power and the start political-economic conditions in Poland contributed to turning these messianic hopes into a practical plan for action. Only a return to Zion could save Jews from these dire circumstances.
This realization was also reinforced by my father's critical view of Jewish life in Poland. Hew was appalled by the neglect of practical education and planning for the future of the younger generation. At that time most religious Jews, especially Hasidim, gave their children only a religious education, leaving their economic future to God, and the results had been disastrous. How many heder teachers, rabbis, shochtim, and other minor religious functionaries could the increasingly impoverished community sustain? He was also troubled by the prejudice against craftsmanship or agriculture that was prevalent among religious Jews, and was dismayed by their preoccupation with tales of miracles attributed to Hasidic leaders and their disregard of the political and economic realities.
A few words with regard to the Jews in Poland. From the moment of crossing the borders of Lithuania, I had remarked in every town and village swarms of people differing entirely from the other inhabitants in physical appearance and costume, and in whose sharply-drawn features, long beards, and flowing dresses, with the coal-black eyes and oriental costumes of the women, I at once recognised the dispersed and wandering children of Israel.
Poland is regarded as their Land of Promise; and there they present a more extraordinary spectacle than in any country where their race is known. Centuries have rolled on, revolutions have convulsed the globe, new and strange opinions have disturbed the human race, but the Polish Jew remains unchanged: the same as the dark superstition of the middle ages made him; the same in his outward appearance and internal dispositions, in his physical and moral condition, as when he fled thither for refuge from the swords of the crusaders.
While in Germany, Italy, Spain, Portugal, and even in England and France, their whole history is that of one continued persecution, oppressed by the nobles, anathematized by the clergy, despised and abhorred by the populace, flying from city to city, arrested, and tortured, and burned alive, and sometimes destroying themselves by thousands to escape horrors worse than death; while all orders were arrayed in fierce and implacable hatred against them, in Poland the race of Israel found rest; and there they remain at this day, after centuries of residence, still a distinct people, strangers and sojourners in the land, mingling with their neighbours in the every-day business of life, but never mingling their blood; the direct descendants of the Israelites who, three thousand years ago, went out from the land of Egypt; speaking the same language, and practising the laws delivered to Moses on the mountain of Sinai; mourning over their fallen temple, and still looking for the Messiah who shall bring together their scattered nation and restore their temporal kingdom.
more from Incidents, some of the other Jews, in this case the nouveau riche:But notwithstanding the interest of their history and position, the Polish Jews are far from being an interesting people; they swarm about the villages and towns, intent on gain, and monopolizing all the petty traffic of the country. Outward degradation has worked inward upon their minds; confined to base and sordid occupations, their thoughts and feelings are contracted to their stations, and the despised have become despicable. It was principally in his capacity of innkeeper that I became acquainted with the Polish Jew. The inn is generally a miserable hovel communicating with, or a room partitioned off in one corner of, a large shed serving as a stable and yard for vehicles; the entrance is under a low porch of timber; the floor is of dirt; the furniture consists of a long table, or two or three small ones, and in one corner a bunch of straw, or sometimes a few raised boards formed into a platform, with straw spread over it, for beds; at one end a narrow door leads into a sort of hole filled with dirty beds, old women, half-grown boys and girls, and children not overburdened with garments, and so filthy that, however fatigued, I never felt disposed to venture among them for rest. Here the Jew, assisted by a dirty-faced Rachel, with a keen and anxious look, passes his whole day in serving out to the meanest customers beer, and hay, and corn; wrangling with and extorting money from intoxicated peasants; and, it is said, sometimes, after the day's drudgery is over, retires at night to his miserable hole to pore over the ponderous volumes filled with rabbinical lore; or sometimes his mind takes a higher flight, meditating upon the nature of the human soul; its relation to the Divinity; the connection between the spirit and the body; and indulging in the visionary hope of gaining, by means of cabalistic formula, command over the spirits of the air, the fire, the flood, and the earth.
The principal public garden in Warsaw. It stands in the very heart of the city [...]. It is enclosed all around by high brick walls, screened by shrubs, and vines, and trees rising above, so as to exclude the view of the houses facing it. It is handsomely laid out with lawns and gravel-walks, and adorned with trees; and as the grounds are exceedingly rural and picturesque, and the high walls and trees completely shut out the view of all surrounding objects, I could hardly realize that I was in the centre of a populous city.
before the revolution, it had always been thronged by a gay and brilliant collection of the nobility of Warsaw; and he enumerated several families whose names were identified with the history of Poland, who were in the habit of being there at a certain time, as regularly as the trees which then shaded our walk; but since the revolution these families were broken up and dispersed, and their principal members dead or in exile, or else lived retired, too proud in their fallen state to exhibit themselves in public places, where they were liable to be insulted by the presence of their Russian conquerors.
I had noticed one party, a dark, pale, and interesting-looking man, with an elegant lady and several children and servants, as possessing, altogether, a singularly melancholy and aristocratic appearance; but the interest I was disposed to take in them was speedily dispelled by hearing that he was a baptized Jew, a money broker, who had accumulated a fortune by taking advantage of the necessities of the distressed nobles. Indeed, next to the Russian officers, the baptized Jews were the most prominent persons on the promenade. These persons form a peculiar class in Warsaw, occupying a position between the Israelites and Christians, and amalgamating with neither. Many of them are rich, well educated, and accomplished, and possess great elegance of appearance and manner. They hate most cordially their unregenerated brethren, and it is unnecessary to say that this hate is abundantly reciprocated.