... similarly 8 track cartridges, before cassettes, the ultimate piece of crap, were initially made for use in radio stations for advertisements (not much tape (i.e. less weight thus less force/abuse involved), And a moving head with serious alignment problems. But, their PORTABILITY was a revolution! 8 tracks were meant to be thrown away when that ad campaign was over ...
That is not correct. Broadcast carts are similar to 8-track cartridges but have some distinct differences. First, they run at 7.5 ips. (And some ran at 15 ips.) Unlike the 8-track, the broadcast cart has no rubber roller. Instead, the roller pivots up into the cart from the player itself, and then presses the tape against the capstan. Also unlike 8-track, tape heads are fixed in cart machine.
Most cart machines were either mono with a second track reserved for cue tones, or 2-track stereo with a third track for the cue tones. And they weren’t disposable, but were bulk erased and re-used.
The best cart machines were very, very good.