Because people eager to please will post mirrors/copies and YC's very pragmatic in-house legal team has (likely) decided that those people bear the legal responsibility of doing that, or at least that YC's exposure is limited under certain circumstances.

That would likely mean that they will give out the poster's email/IP given just a credible threat of a lawsuit.

So maybe don't post these if you live in a country where copyright is actively enforced.

Newspapers/magazines generally don't go after copyright infringements on an article level, I think, but who knows what might happen in the current economic downturn.

I think it's (likely) unethical of YC to routinely and obviously allow these links, for the reasons outlined above. Not because I care for the publishers, but because of the potential harm YC exposes its users to by normalizing this.

(a) Why wouldn’t they be? (2) Someone usually posts an archive.ph workaround within minutes after posting.