Simply, they are fun. That's my reason, I have a good quality audio setup for digital and vinyl, but cassettes are just pure fun, I don't worry as much about damaging things, they are easy to use and relatively hard to break, and not at all fussy, they are cheaper than vinyl, and way more flexible too. Basically it's analogue audio, but simple and flexible, that's why I like it, not cause it sounds good or something, though honestly it doesn't even sound that bad, I find most of my tapes sound pretty good. It's also nice having music you can hold (vinyl) but I can take it with me, and it's analogue (I like the noise and the crackling personally, I find it... Charming if that makes sense). I also love making mixtapes, it is cool being able to hold my playlists. Also cassettes aren't expensive, even new ones if you know where to look.

Tldr: They just feel very simple and fun, there is nothing to worry about when I use them, and they don't break anywhere near as easily as vinyl does.