When I was a kid and I was told to write an essay "what is slop" teachers would give lots of extra points for dumping useless and somehow vaguely related information just to raise the word count. Answers along "slop is useless shit created only to serve as filler content to make money on stupid people" would get zero points, I was expected to write the history of slop, the etymology of the word, the cultural context, the projected future, blah blah blah, don't forget at least ten citations, even if they're even more useless than the essay I was writing and 100% pure unadulterated slop.

My master's thesis was on a topic that nobody else researched (it wasn't revolutionary, just a fun novel gimmick), so I had to write filler just to have a chapter on a topic possible to find references to, in order to get the citations count, even if the chapter wasn't relevant to the actual topic of the thesis

So yes, I think that the push to create slop was there even before computers became a thing, we just didn't recognize it