FAANG looks good on the resume so people go there with intention to eventually leave for another company willing to pay for FAANG experience. unless you work in a very focused team (e. g Occulus) youre better off jumping companies for higher pay.

if you go to tech career fairs, especially in the silicon valley, the biggest example of this is working for Cisco. they have huge turnover and youre only going to work there to have Cisco on your resume because of how ubiquitous they are at networking for companies.