Why is it? You don't get to censor important sources of information and then literally just cite "why not?" as the reason.

The linked wiki page lists the reasons. You can't just say these are not good reasons without saying why

Which one of them justifies the government putting you in prison for accessing the information?

“Protecting democracy” or something Orwellian like that

archive.is protects democracy and that's why it must be illegal to access?

I mean that’s probably what they believe, the idea is to shape favored outcomes by denying their voters access to information.

Unironically, yes.

Censorship is bad, also it is always slippery slope.

Additionally it is against Article 19 of the Universal Declaration of Human Rights of the UN. And Article 20 of the Spanish Constitution.