Tbh, I do get why they do instruction booklets and stuff only for collectors editions.

Back in the 90s and before that instruction booklets were actually vitally important. Games just didn't have the storage size to cram decent tutorials, backstory and artwork into the game itself. The booklets taught you how to play the game and gave you nice images to visualize what the 16 pixels that made up your character were supposed to symbolize.

All that isn't necessary anymore. In-game tutorials and resources are much better than what you could pack into a booklet (and can be updated, which isn't possible with the booklet), and hardware advances mean that the games look exactly how they are supposed to look. Artwork in the booklet wouldn't look any better.

But some people love that kind of stuff, so it makes sense to sell it only to them and save the money and material that would just go into the bin for most buyers.