OK, a quick google showed me that 45 minute cassettes go for about 44 cents each in bulk, plus 28 cents for a case.
CD's are about 22 cents each, plus 10 cents for the case.
We can consider the art/insert to be a wash -- should cost roughly the same for cassette or CD. I'd guess that labor on reproducing a cassette would be more too, if only because it takes longer to do. But I haven't documented that so we can leave it out. So about 75 cents for a cassette versus 32 cents for a CD. Twice as much.
Are you seriously suggesting that cassette players are more available that CD players? Seriously? I mean, cassette decks haven't been made for the mass market in about 20 years. Every laptop and desktop computer has a CD player in it. Most vehicles made since about 1990 have CD players.
And surely you aren't suggesting you get better music quality off a cassette. I mean, even before the thing starts disintegrating and getting dropouts, the sound quality is nowhere near a CD. And maybe you like rewinding and fast-forwarding to get to the song you want.
And, as you say, nobody even uses CD's anymore. If there's no good reason to use CD's now, it makes even less sense to go back to an even older and less versatile technology.
it is the cheapest way to produce something their target market will buy
This is a good explanation of why a band would sell them. They sell them because people will buy them. Still doesn't answer the real question -- why the fuck would anybody buy music cassettes in this day and age?
So, I'm right back to where I started:
Are cassettes:
Cheaper -- No.
Easier to use -- No.
Better sound quality -- No.
Do they help you look cool to the other young whippersnappers? -- Yep.
Pretense.