[coldtea]

>And I’ve been wondering why would anyone buy the cassette or CD?

Many people I know buy the CD because they prefer owning a physical medium, and the CDs they actually play and have a collection of them.

As for cassette, I don't know about buying regular releases on it, but there's a small but very passionate music community around cassette releases for experimental and indie music (same as a demoscene using old computers or people making new 8bit games).