As a long time (I start Medicare this year) low-fi audiophile, I wanted to bring up a couple points on the topic.
Cassettes are not always used as a source for music. Many of us are into recordings of the spoken word and cassettes have always had enough fidelity for that. I've been a collector of radio programs (anything from the 1920s to present) for many years and cassettes (and reel-to-reel) have been well-suited to that hobby. That said, yes, I am digitizing my collections for both backup and random-access purposes but I still do use my cassette playing equipment (Nakamichi and Sony) for casual listening.
Regarding 8-track tapes, yes, they were really the best solution for the automobile application in their day. But I would like to mention they had a competing format, the 4-track cartridge. The technology was similar to the 8-track except that, unlike the 8-track cartridge with contained the pinch roller, in 4-tracks the pinch roller was in the player and inserted itself into an opening in the bottom of the cartridge when it was placed into the player. Also, the 4-track and only 2 program selections as opposed to the 8-track's 4. I have a working combination 4- and 8-track player by Muntz mounted under dash in my 1959 Volvo.
BTW, one can still buy belts for these players and repair parts (foil splicing tape, pressure pads, etc.) for the cartridges.