<cynical view> When a _customer_ requests data to be deleted, you delete it. Pretty sure Facebook have probably complied with every user-data-deletion request they've ever got from their paying customers - because advertisers are well know for wanting access to less data about the cattle...

I doubt that advertisers requesting to have all their information deleted (apart from tax relevant data) would be more successful.

Fuck their paying customers

That's not true. What if you want to support un-delete? That's a reason.

To my knowledge there is and has never been any option to “undelete” your deleted content on Facebook.

I'd be surprised if there wasn't at least a way to deal with large-scale account hijacking, where the hijacker deleted lots of hijacked accounts' content.

Mm, what about deactivated accounts? You can reactivate them, which would involve undeleting data.

Yes there are, but there are no moral reasons to not comply with it.

If your ethics are such that you believe the state should be able to view data on someone in order to help prosecution of a crime then you could support the retention of data on all users in order to avoid deletions made to hide criminal activity.

Such an ethic creates a moral reasoning to not comply with an individual's wishes in the immediate deletion of data.

(FWIW I'm not defending this position nor suggesting it's the case here, just you said there's no moral reason that can support it, which seems wrong; different ethical systems can provide different reasoned moral outcomes.)

Why, to help people connect better of course...

There might be something to that, in the sense that I could very well see someone in a meeting ask 'well, but what do we do when another user is tagged in a photo' followed by discussion rationalising why that person shouldn't lose out because someone wants to delete data, and someone coming up with the 'solution' of effectively reference counting the data and figuring out when to actually purge the underlying file later (i.e. never)