Where I live, lots of used cassettes - pre-recorded and good quality home-recorded - are available at thrift stores, but don't get picked. Vinyl is popular, however. I snag plenty of tapes and some of those are typically large drop-offs from the previous owner. I gave away a lot of my pre-recorded tapes years ago, and now I find myself picking up used ones, but mostly titles I don't have in any other format.
Yes, cassette tapes are becoming popular, again.
Nando.