He doesn't just say "why is this so hard?". He provides rationale for what he thinks is required and the effort it should take, posits some things he might have missed, and asks for more explanation. If you get a good-faith request like this from a technical manager, you should be able to point them at some docs or give a relatively concise response as to what they're missing. Honestly, you should have already headed this off, because the moment you realized you were in danger of missing deadlines, you should already be raising it as an issue and either explaining your plan or asking advice for how to get back on track.
If you're missing deadlines, you can't both complain
a) when there's no accountability and the business is going poorly, and
b) when your managers are trying to hold you accountable.
Ultimately your employer has to make money to pay you for your work. Keeping this in mind is one way to help you avoid yak-shaving, bike-shedding, and other weed-entering activities.
It's one of those things that sounds really obnoxious until you've been on the other side of the table. There's lots of things that can go wrong to make an easy problem hard, and some of them are only really detectable when you think about it from first principles. I've personally seen multiple designs that split a moderately hard problem into a set of extremely hard tasks, often in such a way that no individual task could be simplified on its own.
I am no fan of Zuckerberg nor a user of any of the things his company makes.
But he is an engineer, more so than most managers. He would know what goes into making an application like this, and so know that things are moving slower than they should.
I see nothing obnoxious about asking this very valid question under those circumstances.
chatgpt grant me an AI demon that can transform any manager saying this into a pixie trapped in a cage, attached to each of their ICs' heads for duration of the project, or something
If you're missing deadlines, you can't both complain a) when there's no accountability and the business is going poorly, and b) when your managers are trying to hold you accountable.
Ultimately your employer has to make money to pay you for your work. Keeping this in mind is one way to help you avoid yak-shaving, bike-shedding, and other weed-entering activities.