Why is this being downvoted? I didn't know it either, and it also improves my perception of FB as a company.
They had to refuse. They needed to grow their talent pool. The others were focused on defending against msft.
It is well known and was in the same pile of court discovery leaks
FB has always been good to employees. Much like Microsoft (comparatively).
The number of amoral geniuses purely driven by technical challenge is limited. Businesses making money on the edge of ethics have to treat their employees well to keep them. When there is no "big lofty goal", you need to get people motivated someway. Adtech, fintech, crypto...