If there was any online component, they could always take down the servers. Or if the game was broken from the start or became broken at any point, they could always just never provide the necessary update to make it playable.
Digital only just makes those problems apply to all games.
I've never really been one to sell my games because I'm always wanting to go back and play them later, so I can't really offer any input on that fact.
I like playing a collection too, and I was able to acquire it because other people where able to sell/give away theirs
I just prefer the system that gives me at least a paper thin guarantee over the one that's less convenient and has absolutely no guarantee.
Being able to physically hold everything needed to play the game was our guarantee.
A guarantee the publisher would never ever be able to take what we had just paid $60 (or less, secondhand) away from us.