"What if" scenarios. It's definitely happened on other store fronts and likely has on steam at some point. Is it something they do on a daily basis? No. Is it something to be concerned in about in the long term since they're often not giving you a refund? Yes. Sure you have your downloaded copy, but if something happens to that copy, there's a solid chance you're SOL unless you're sailing the high seas for an alternate copy.
I mean, what are the chances that Steam takes away my game (for some reason? That's never adequately explained either) AND then I lose my hard copy?
A heck of a lot lower than any of the other things that could take away my games, I'll tell you that much. I've lost games before, and most of it happened back when they were still on CD. I've yet to permanently lose a game I bought off any distribution platform, much less Steam in particular.
It just strikes me as fearmongering. The Government could come kick down my door and confiscate all my Puella Magi Madoka Magica manga too, but I'm not really that scared about losing access to Kazumi's inappropriately sexy booty. Tomorrow I could be struck dead in my gamer chair as a semi-truck careens through my bedroom. Next week I could get nuked in an unprovoked nuclear strike by the Chinese.
Sometimes it's important to think about what's likely to happen, rather than what could possibly, in some way, happen.
Not every person keeps every game they own permanently installed, steam has (usually due to the publisher) revoked download privileges in the past (I've lost a few older mainstream games this way), and if this happens and you don't happen to have the game installed at that point in time, you're SOL.
I mean sure. If you keep games in library, undownloaded, then you can have that taken away. But it seems silly, to me, to avoid the platform entirely when it's quite trivial to just... Download the games and have a backup. Consider the alternatives:
Are you going to just download the game off a pirate site? If the site goes down, now you can't redownload it, and pirate sites are generally less reliable than Steam because they're usually illegal or borderline legal. They're also magnets for viruses and malware, and you don't have the guarantee of a professional company reimbursing you if someone slips something malicious into your download.
Are you going to use another distributor? Now you just have the issues of Steam with a different label. Some of them don't even fully download the games, or install DRM that prevents you from playing offline, so now you're in a worse position.
Are you going to not get the game at all? Well, now you're not playing the game. In order to stop yourself from losing access to the game, you've forgone access to the game. Very intelligent.
I just don't understand the logic here. I've used all kinds of distributors, from physical game stores and pawn shops to Epic and Ubisoft's platforms to Steam and Good Old Games, and honestly Steam is the most robust one I've yet to find. Between it and GoG Galaxy the only reason I even open Epic's program any more is to run Unreal Engine 5 for development purposes.