Along with my giant lp collection used both as leisure and business as a vendor. I also collected a large amount of cassette soundtracks. in which I also sold on my vending tables over the years. Matter of fact I still have many sealed copies of DELERUE, BARRY MORRICONE,ETC ETC soundtracks on cassettes.
Also bought 8-Tracks and I remember getting Goldsmith's QB VII. With the extra bonus that my Dad had an 8-Track Player in his Chrysler Town & Country Station Wagon. I think I was the only kid ever blasting Goldsmith's Emmy Winning Score, cruising down the streets of San Jose. Well, not blasting. Dad did have some rules. I had PATTON on 8-Track too!
The first soundtracks I owned were the Star Wars trilogy cassettes. I also had Indiana Jones Temple of Doom & Last Crusade on tape, and Jurassic Park. It wasn't that long after I started listening to scores on their own that I got a CD player, so I don't have that many tapes. Once I started building my CD collection though, I would make lots of mix tapes especially for use in the car, since that was before CD burners became commonplace, and cars didn't come with CD players yet. I still have a shoebox full of mix tapes buried in a closet somewhere.
I think there popularity were there convenience. The first gadget besides a transistor radio in which you travel with your music. The late 70's the JAPANESE came up with the Walkman and one could listen to the music they want wherever they went. Even the subways, where radio receptions were impossible. It was very helpful for people on the go. God knows how many soundtracks I listen to on the way to work and back in the 80's on subways, buses or walking.
Yeah, I bought my very first score on cassette, Jurassic Park, on 1993 or maybe 1994. Along with some non-film music, I think I had also 1492 by Vangelis. Fortunately, I made the transition to CD a few months later.
Only film music I ever bought on cassette was on the Arcade label and it was Hollywood Greats. In the 70s Arcade and K-Tell used to advertise 20 track LPs of various kinds, usually chart pop music. And here was a collection of my favourite musical numbers including Singin' in the Rain.
But in a way cassettes were my intro to film music collecting, as a kid, as I recorded lots of movie and tv themes direct off tv with the recorder's microphone pointing at the telly (as we Brits call it). This meant that some had the neighbour's dog barking, folks knocking at the door etc.
When I was old enough to buy my own stuff, I made many compilations of movie music on cassette for my friends to show how good it was, and not just 'background' music, as many non-film music appear to think it is.