> Why don't we instead just auction off visas to improve efficiency?

The areas with lower cost and wages can't compete attracting local talent, but auctions would make it even harder for them to attract foreign talent as well. It's a losing proposition for pretty much everyone.

Do you think they have a problem finding 2,000 if they are paying market rate, or can you suspect that this is seen as a cheap alternative for getting equivalently skilled people at a lower cost?

Facebook tends to be one of the highest payers in industry. It's possible paying even higher would net more people, but overall math suggests the best N people won't necessary be US citizens or permanent residents.

The law doesn't say you can hire the best person if they are abroad though.

It effectively says you can't hire a better person from abroad if there is a person who is good-enough domestically.

(I'm only saying what the law says, not what is best for Facebook, the USA, or even what is morally right)

"qualified" is completely arbitrary. I can just set the threshold high enough such that there aren't enough "qualified" people domestically.