1. Not all that convenient.
Let's face it, the only reason any of us bought cassettes back in the day was so that we could play our music on-the-go, which you most certainly could not do with vinyl, although some have definitely tried over the years. But did you ever try running with a Walkman? Total pain in the ass.
In order for there to be a nostalgic resurgence, though, the device-in-question must retain a certain coolness and, well, cassettes were never cool; not if you wanted to hear a specific song right away. Anyone who looks back upon cassettes with any fondness whatsoever conveniently forgets how much time they spent fast-forwarding or rewinding to get to the song they wanted to hear.
2. Poor sound quality.
Grab one of your thirty-year-old cassettes and put it in the nearest cassette player. Chances are the first thing you'll notice during your musical walk down memory lane is how annoying tape hiss, wow and flutter, and other artifacts were "back in the day".
Making matters worse, two different players might play cassettes at two speeds, so, depending on the player, you might actually get to hear Mickey Mouse sing your favorite Smiths song. As durable as cassettes may have been, very few people could be bothered to perform even the most basic maintenance on their cassette players. Head cleaner, anyone?
3. Nobody really likes mix tapes.
I hate to burst your bubble, but the only folks who look back fondly upon mix tapes are the ones who were always forcing their mix tapes upon unsuspecting friends and would-be lovers. We had it in our heads that if we took the time to painstakingly select the right songs, put them in the perfect order, and then place said cassette tape in the hands of Susie McSwizzlestick that her clothing might magically fly off. That five minutes later her clothes would fly off in exchange for a ride home in the back of Jock Brewster's pickup truck, well, it definitely helped put things in their proper perspective.
4. Hmm, tapes melt, go figure.
While it was awesome being able to play your own music in the car, it wasn't so fun if you accidentally left your cassette copy of Get Lucky on the front seat in, say, the middle of August. By the time you finished your shift at Chess King and hopped in your 1981 Honda Civic to join your friends at the lake, your Loverboy tape looked like one of Salvador Dali's pocket watches.
5. Good luck reading those liner notes.
Back when folks actually cared enough about music to read the liner notes, albums were full of information. If you wanted to know who played bass on "Walk On The Wild Side", you just flipped the album over, or found the info on the inner sleeve in a font large enough to read without the need for space-age magnification. Cassettes, on the other hand, either contained full album credits in a microscopic font that even the Hubble telescope couldn't read clearly or did away with them entirely.