It is actually very difficult to get an initial H-1B worker, since the worker has to get selected in a lottery, and the company has to wait 7 months.[1] The odds of getting picked in the H1B lottery is around 32% as of 2020. The 7-month wait time itself massively disincentivizes employers from hiring non-US workers. The end result is that most of H1B sponsorships go to people already in the US on a student visa who are working for the company using a status called "F-1 OPT". It's quite difficult to get hired from abroad. Many larger companies still do it, and are willing to wait 7 months, but the wait 7-month time and uncertain nature of the lottery are significant factors that discourage companies from hiring non-US workers.

For out-of-US hires, Facebook will actually get you a Canadian work visa, and have you work in Canada for the 7 month wait, and potentially for year if you don't get picked in the lottery. The strategy for multiple large firms is to bring non-US workers to Canada first, and then try to move them over to the US, since US immigration law is extraordinarily restrictive compared to most countries.

[1] The company applies for the worker in March of the year, and if the individual is picked in the lottery, they get to start working for them in October.