I don't have this problem in the genres I listen to--they have only not had a couple of songs from pretty obscure groups.

Even when I create a station by artist, say The Avett Brothers (considered folk music, I believe), I end up getting repeats quickly--even among the non-Avett artists playing on the station.

My own personal folk playlist (on spotify) has more variety than their own station.

I'm convinced it's an algorithm issue in my case. In yours, possibly lack of choices.