It has became very obvious how reliant we are on Archive.org last time they had an extended outage (remember?, they got hacked,then they couldn't bring the system back up for weeks and weeks). Huge amounts of reference material suddenly dissappeared.
Personally I think it is a huge error we don't force archive.org to allow others to mirror their data easily.
The problem with this is that there's all kinds of user-generated web content that certain people wouldn't want tax dollars going towards preserving.
I can already look at e.g. the National Film Registry and say I don't care about movies so my tax dollars shouldn't go towards preserving them, regardless of what some bureaucrat thinks is "culturally significant." The film industry has a pretty massive network of artists who are able to go to bat for that stuff, though.
But then take pornography, or hate speech (and/or straight-up misinformation), or content that's illegal in the US but not elsewhere (like drug recipes or weapons schematics). It's already tricky for a private entity to handle convincing people of the value of preserving everything physically and legally possible to preserve. Making an argument for doing it as a public function, even in good faith, could easily turn into a mess-- especially when we can barely agree what should be allowed on the internet now.
Personally I think it is a huge error we don't force archive.org to allow others to mirror their data easily.