Same reason people work at any of these big companies, money and prestige. You can be a terrible engineer, but if you have a few years experience at Meta it's going to make people think you must be a great one.
It's like you are saying you worked at Microsoft, Oracle, HP or Cisco. Who wants to hire such people?
I am much happier not working there though, getting laid off was a relief. Things changed a lot after the first layoffs and when the stock was around $90!