Closed doesn't have to mean resolved and the tickets would still be available either way. Closed is IMO ideal for these tickets as ultimately it means that they aren't being looked at.
Whether any given ticket is being looked at can change over time. Closing it is a way to drastically reduce the likelihood that it is being looked at. As a user, I see no good reason why that should be done, in particular when it is applied across the board without considering the individual issue.
As a user you obviously see no good reason for that. As maintainers having more bugs open than will ever be worked on (e.g. because no one will put up the legwork), serves no good purpose.
PS: individually considering each of 100s of issues takes time and mind share, that can better be invested elsewhere.
If those issues are still a problem nobody will find them, they'll make new issues and lose all the previous history, unless the UI is designed to support automatically suggesting reopening an old issue instead.
A middle-ground might be to leave open the issues with recent activity, with the idea being that at least the ones that are affecting people the most are not swept under the rug.
There's a crucial question here that I find not enough people ask themselves: does that actually matter? And if yes, why? What, specifically, is the material problem caused by this situation?
It often feels like people are just chasing 'inbox zero', under the assumption that "0 open issues == good", without any actual material problem being solved in the process.
(Github probably isn't helping here, with their undeservedly prominent placement of the open issue count driving this sort of behaviour...)