The basic design of the endless-loop cartridge had been around since the early '50s, long before the cassette. Originally developed as a "talking advertisement", it grew into the Fidelipac cartridge which was almost universally used in radio stations for commercials and songs. Those carts worked just fine, because there was roughly only 5 or ten minutes of tape, at most.
Later, a California entrepeneur named Earl Muntz took that same cart, stuffed it full of tape, had Clarion manufacture car players, licensed music from a variety of labels, and sold what became the first car stereos. In the car-crazy culture of California, they became a big hit in a time when your music choices were AM radio (unless you had one of those new-fangled FM adapters). They also started to show up on the east coast, but were still a niche product until they came to the attention of Bill Lear, of Lear Jet fame.
Lear took the basic four-track cartridge, improved on it enough to get several patents, and had magnetic head companies develop an 8 track head, which meant half the tape was needed for an album - and the tape was the most expensive part of the device, not the shell. He sold the idea to Ford, and 8 tracks were introduced in 1964 - at a time when the cassette was still seen as primarily for voice recording, and a strange product from Europe besides.
8 track would always be hampered by its endless-loop design, plus the fact that four cassettes would fit in the space of one 8T, plus the fact that a cassette used even less tape for the same album as an 8T, and less plastic at a time when plastic zoomed in price due to the first oil crisis in 1973-74. It also was primarily designed for playback, not home recording.
Engineers saw that the 8 track was a dead-end, technology-wise, and threw their efforts into improving the cassette instead. The 8 track didn't disappear right away, however; it had almost a 20-year run. Not bad for a home grown, American idea that began as the Cousino Audio Vendor. Look it up!
