The thing is that even if you have what you think is a good story in the beginning, maybe it won't translate well into a 40 hour game. Now you have to tweak it. But maybe you've already spent a year working on a lot of the level design and art assets. Do you scrap a big chunk of it and start over or try to make it work in with some re-writes. God help you if you leave play testing until the end of development and find out that the pacing is atrocious or a level isn't rating very well with testers.
So yeah, game development is a much more complicated beast than it can initially seem. And one of the things that limiting what the developer can do could help with would be letting them prototype, test, and figure out what works much faster. Not to mention making it easier to scrap things that just don't work.
I also happen to believe that when you can't cover up a lackluster story with fancy graphics, cutscenes, and flashy animation and effect it makes it a lot harder to pass off a turd as something decent. But if you have the talent and experience to nail pacing, story, characters, gameplay, etc. in a game with tougher hardware and software limitations, then you can more easily scale that experience up. Again, it forces you to get to the fundamentals and make the entire package work together to convey a great experience since you have so many fewer tools to work with to get that experience across.