Nobody thought to themselves "maybe this zero-rate interest environment will end", or "maybe our business model is losing steam"?
No, instead they went full-on increasing headcount, leaving software engineers scratching their heads on exactly what they were supposed to be doing.
When discussions started about companies "poaching" talent so that others couldn't get them, I saw the writing on the wall. Possibly no role even lined up, but let's just get them onboard and we'll figure that out later.
I'm over 20 years into this career but am not FAANG. I like my boring, predictable companies for some reason, and they like me.
No one in management cares. The hiring and then firing is a feature, not a bug.
It makes a lot of sense when you consider the incentives of all the individuals involved. Individual line managers think "I need more headcount so I can increase my scope of responsibility and get promoted," and go to their directors with "These are all the cool new projects we could be undertaking if only we had headcount." Directors think "If I don't provide career-advancement opportunities for my best managers, they'll leave for a competitor and the best engineers will follow them, and my carefully-constructed org will collapse", then go to finance with "These are all the cool new projects we could be undertaking if only we had budget." Finance people look at the negative real interest rates that were present in 2020-2022, think "Just about any project that has any chance of generating additional usage or revenue beats the 2% nominal and -6% real returns we can get from the market, so these project ideas look pretty good" and tells the CEO "Our best bet is to invest in the company itself, so we are going to greenlight all the headcount requests."
Look at what the business of these companies was. None of them needed this many non-customer-service personnel. But that many people needed jobs.
To be frank, that was my opinion of Facebook before you were hired.
Also, the stock price literally never decreased between when I accepted my offer and when I finished, so clearly I was holding it all together \s.