FB and Google are well known for paying near or at top of market salaries for developers and PMs. Netflix is even more explicit about this - their compensation philosophy (available on their website) can be summarized as "We will not be outbid." (from personal experience I know they really mean it)

These companies sponsor H1B visas because some of the people they wish to hire happen to not able to work in the US without a visa. They'll hire anyone who passes the interview.