Cassette tapes haven't disappeared at all, if anything they're growing in popularity. There's at least five cassette only labels that I know of. I released a cassette album in January, it sold surprisingly well, there's another being released by the same label early next month, and a release is scheduled on a different label in September.
Cassettes are probably quite genre specific. Check out these labels :
https://rustedtonerecordings.bandcamp.com/music
https://softerror.bandcamp.com/album/care-work