I wonder how much of the “1 product in the middle” was simply driven by the fact that sometimes you F*** up your second sketch, and then you risk ruining a perfectly good piece of paper. Or simply due to cleanliness for being able to pin something up for a client “heres a wall of concepts, 1 per page”
I feel like college and portfolio presentations reinforced the “Fill a sheet with ideas and it’ll show how good you are at ideation” mentality, but even I used to dread when I would start adding different callouts to a drawing then slip with the marker and have to fix it all in photoshop. That wasn’t a luxury back then.