Why so many of I. B. Singer's stories seem the same

Reading through (with many skips) the Library of America first volume of the stories of Isaac Bashevis Singer it's truly astonishing how often he goes to the well for stories about possession, spirits, dybbuks, and demons of all sorts; as noted in yesterday's post, many (but not all) of these stories portray women in a frightful manner - many of Singer's female characters are exceptionally powerful, but their power comes from dark forces and they often use the power in destructive ways. Reading through some of the stories collected in his 3rd volume of English translations, Short Friday, from the mid 1960s, two further things strike me: it's amazing how little of his material up to this point in his career comes from his years in the States, 25 years or so at that point in his life. Though I haven't read each of the translated stories up to that point, it seems that only one out of the 40 or so takes place entirely in the U.S. and one other concludes in the U.S. Also striking is how few of his stories are naturalistic, that is, include no elements of spiritualism, magic, possession, or surrealism - and yet, these are perhaps his best-known and best stories: Gimpel the Fool for one, also The Little Shoemakers (maybe not among his best known and maybe it's my own biases and preferences that rank it among his best), and Yentl the Yeshiva Girl (didn't re-read it, but I think it has no supernatural elements - and certainly his most profitable story). Why didn't his style mature or evolve over these years (it did later, to a degree)? I'd say in part because he was a working writer or a sort that no longer exists - publishing his stories in the daily Yiddish press, publishing the translations in the many magazines that existed then than made a market for fiction: Commentary, Saturday Evening Post, later The New Yorker, all but the latter gone or no longer in the market. But Singer was providing product for a market that paid very well - he had to meet his quota to pay his bills. The great thing about the system of those days is that a talented writer could make a living as a "man of letters," but the sad thing is that it discouraged innovation, risk-taking, and growth - encouraged repetition of successful and profitable formulaic writing, even if of a high order. Today, an I B Singer would hold a chair in a university and could publish whatever the hell he'd like, or not at all - and in some ways that's bad too: an over-emphasis on the obscure and unconventional, an inner focus on the world of academe and of ideas, a lack of exposure to the varieties of life - all of these forces have stunted or derailed many talents.