Well there’s a few things for early at home games, for one the instruction booklets were actually worth a damn, often containing the story, tutorial, and more. Also, size was at much more of a premium, so since instruction manuals were a thing, it was considered a waste to have all of that stuff in the game itself. I’m sure there are exceptions but that’s the general idea.
Much as I lament the loss of good instruction manuals, it’s understandable why they went away in light of why they were necessary before.