They do it because the money, though. I turned down a FAANG job partly because I'd have to relocate across the US and partly because I didn't think I could sleep at night working for them. Total compensation package for first year was $250-350K depending on performance, and there was a signing bonus. This was 2015 or so.
I often half regret that decision, because it hurts to know I could've ticked that income box rather than fighting month after month to keep work coming in (self employed/contractor).