Non-Prog Used Records

I think this is the first new discussion topic I've posted here on Prog Archives.  It was suggested by a recent discussion in the Prog Lounge section about finding unfamiliar prog records and cassettes at thrift shops, used record stores, etc.  However, my discussion is not strictly about progressive rock.  When I still had a working turntable and collected records, I used to find a lot more classical and jazz records than progressive rock.  My theory on the reason for this is that a much wider variety of interpretations of jazz and classical compositions is released by record companies.  Therefore, it makes sense that someone who was looking for specific music would have an easier time finding what he or she was looking for.  Has this been anyone else's experience, and do you have other explanations as to why this is the case?