A big factor for not doing that (besides the cost of employing a helpdesk for every language that Facebook is used in) is that the helpdesk just becomes another vector for malicious account takeover. If you put it there, you're going to have sob stories about people who made their account years ago but don't have the old password, don't have access to the email, don't remember what they posted, and yet will cry, expecting the human on the other end to give their their FB account back - and if they can do that, so can a malicious actor trying to get into random peoples' accounts to scam then on Marketplace[0] or what have you.
I understand the business factors that require initial account creation to be frictionless, and so why proof of identity must be weak, but why can't account recovery offer an option where you prove your identity indisputably?
For example, some sort of physical storefront (possibly run by an independent company), where you go and say I am so-and-so and here's my ID and please take my picture and my fingerprints so that if I'm scamming I'll be easy to catch and here's twenty bucks for your trouble.
I'd rather do that then spend weeks or months locked out, uncertain, and talking to a wall.
Privacy advocates won't be happy, but Facebook, Google, etc. don't have the same motivations as privacy advocates.
That is essentially what mobile phone carriers do, yet "customers" provide fake/stolen IDs all the time to perform sim-swap attacks and obtain financed phones they never plan to make a payment on.
Germany has a suitable system built on an NFC chip in the federal ID (Personalausweis).
When you get it (renewed), you get a transport pin, which you can use to set a regular usage pin, which you can then use to auth yourself to the NFC chip and make it provide some signed information to the remote end.
Also, they are not particularly easy to fake to a degree that passes spot checks, anyways.
Facebook does sometimes ask for a scan of government ID in the account recovery flow. Unfortunately the cost of operating the ~100,000 storefronts required to be nearby a significant fraction of its users would be absurd compared to the benefits.
That is a good argument.
But what is with not having a way to put recovery email/phone back to what it was, literally minutes after it was changed by a new login in another state.
0: https://news.ycombinator.com/item?id=28918834