Only if the game personally insulted or betrayed me somehow. For common folk this is unlikely but I could see it happening to a famous person.

It could be very irritating to purchase a game for your amusement and then discover you're a punchline to a joke.

Poor research before buying Way too much hype about building rockets (which seemed amusing, although it's not as educational about real rockets as the hype would lead you belive). I didn't realize it was also a simplified flight simulator (which I don't like). There are apparently mods that make the flight simulator bit easier, but it isn't worth my time.

I think it will be too much hassle for online stores to allow users to permanently delete games and then later regret that decision and then the online store has to reinstate the game into the users library. Being able to hide to game should be enough.

Consider your spouse / life partner wants to leave you and you don't know it and kept the PC on and logged in.
A: I'm leaving you.
B: I don't care, I have my games.
A: You had, lol CU, loser...

Edit:
By that I mean if deleting games is possible, it shouldn't be done with just two mouse clicks.

Just thinking this

Steam offers this option

I would've bought Thronebreaker, and still would, if GWENT and the accompanying GWENT-related material were unbundled from it. As it stands, I do not want GWENT in my library, even hidden. So, GOG lost a sale on Thronebreaker.

I bet they don't care at all , I wouldn't.

They definitely do care about Thronebreaker sales in general; maybe you missed half a year(?) of it being featured on the "Store" tab. Or how they sold it on Scheme after a few weeks since (I assume) it didn't meet sales expectations here when originally it was to be exclusive. Thronebreaker not selling enough here is likely why they wouldn't make Cyberpunk an exclusive here, which negatively affects all of us who care about shopping on this store since an exclusive Cyberpunk (or equivalent big CDPR release) would've been the console equivalent of a "system seller" in getting more people to come here and shop.

Game sales they care, but I think they don't care about your special case, you want Thronebreaker but not Gwent even if you could hide it. I think there are no more than a dozen with a similar problem.
Oh yeah, Cyberpunk would be a system seller, but GoG is just a store, not a whole system , nobody is locked here with 300+$ purchase.

Hoarders gonna hoard.

HIding doesn't work for this purpose in the new interface. "Hidden" games go into their own very prominent category, on par with "updated"; the difference is they aren't in the main category any longer. It works for games you completed, but not for games you want to forget you ever had.

And there's a counter. So if you're using Hidden Games to hide garbage, there's a constant reminder for exactly how many atrocities you bought, how many times GOG """tricked you""" into buying garbage. This can't be good for business.

Previously, there used to be an inobtrusive link at the bottom of the collection. But people were accidentally hiding good games, then couldn't recover them, and complained on the forums.

If I were the UI designer, I'd make a "delete game" - "are you sure" - "are you absolutely sure" option in Library and exclude thusly deleted games from all Library views, and a "recover purchases" option in Purchases, away from Library, which would restore them.

"Only get what you like" is not good advice from a digital DRM-free store to a customer, because how would I know what I like without trying, eh? And after that hurdle is cleared, there's not much incentive to buy.

That's actually such a great idea that it boggles my mind why it isn't implemented yet.

You watch videos and read some reviews get some info before buy, not just buy everything instantly you think will be fun. But it looks like restricting yourself is too much to ask nowadays.

There are times when you go through all the trailers, gameplays, reviews, comments etc - they are all positive, game seems fine and it still just doesn't click with you (Not on GOG but I had exactly that with Red Dead Redemption 2).

Not to mention that people would probably want to "delete" games this way for plethora of other reasons too.