FAANG pays orders of magnitudes better, has better benefits, has flexible work locations and schedules, is working on the most leading edge stuff (autonomous everything, AR, VR, GreenTech etc...) contributes to FOSS, gives leadership opportunities etc...
I'm not sure when this shift happened, but I do remember the tipping point in 2016 when Apple recruited the best PhD away from my company after 6 tries and gave him a 3x pay raise (400k/yr - what startup can afford that for one person?), with the ability to work on self-driving cars.
I'm not sure how it would be possible to compete with that, and don't blame him for leaving.