This may be an intentional decision to cooperate with law enforcement. If they only go silent in the case of ongoing investigations, then "Google went silent" functions in the same way as "the warrant canary disappeared" does for other sites, which could in theory jeopardize an investigation.
You can rest assured, if it was child porn, they'd be obligued to keep backups as proof for law enforcement. I doubt the material is actually deleted, just hidden until they sort it out with the feds.
That's what you get for not making backups. This isn't rocket science. You're using someone else's free service, and they have zero obligation to continue to provide that service to you. Even if they didn't intentionally delete your account, mistakes do happen sometimes. Who actually thinks it's a good idea to keep only one copy of data that you value? Especially on a site with the name "Hacker News"? Do hackers these days not understand backups?
Hell, I've hosted most of my personal domains' email accounts via Google. A few months ago one of them was deleted. I never really used the email, but I certainly had things on their I would like to have for posterity. When Google deleted the account I was given no recourse or ability to appeal. It was just gone. It's not as if the account was even anything controversial, it was just my contact-me email for an old NES modding site I had.