When you search about a Neovim issue for example, often the solution is in an old Reddit thread. When you delete that, it will be gone forever.
And someone might say "I won't post it there", but once the person leaves some info in that site, they're encouraging others to interact with it, and generate more info there, in that walled garden, instead of somewhere else.
Note that the potential of information loss in Reddit does not come just from users deleting their stuff. It's also mods (including automod) and Reddit Inc. itself. One day Reddit will decide "we're going to flush out old content!", and here goes your info anyway, no matter if you deleted it or not. Or Reddit itself will go off, and the info in it will be lost, just like the info from the forums that Reddit itself killed. That's the main reasoning in the link that I've provided, and you know what, I think that the author is 100% right.
Also note that there are ways to reduce the information loss. People can - and IMHO they should - migrate that info, before removing it from Reddit.
I think that you're looking at the info present there _now_ in a short-sighted way, without realising the consequences elsewhere.
EDIT: and as another commenter highlighted everything has been archived already. The info loss will be way, way lower than you think.
Agreed. In the past 2 days I've been overly annoyed as both days I've had multiple google queries dump me to seemingly useful threads that I can not see because of this foolish nonsense of shuttering communities in "protest".