Some people like disc cases and the actual disk itself, but the main gripes I've seen with digital only games on consoles were: 1) without a disc you can't give/trade/sell the game, 2) without a disc the game can be taken away from you, 3) if you can't make an offline backup copy of the game and transfer it from console to console, most/every copy of a game will eventually disappear.

Steam has issues, and you certainly can't (legally) trade or sell your library, but nearly no single player games on the platform have DRM. Thus, you can have as many off-Steam backups as you want (which can't be remotely deleted/disabled), and you could certainly "give" the game to a friend (but don't copy that floppy), or otherwise preserve it for posterity.

You could buy, sell, trade, loan, and backup games with the right regulation. Discs are irrelevant.