A lot of those are going to be contractors employed by agencies.
Google also outsources SWEs. My friend in Mexico worked as this. They have an acronym for this kind of worker, I can't remember. But for example, they contract out work to SWEs at https://www.epam.com.
Not contradicting your point really, just a note
TVC
Yes! Can't believe I forgot. He was an interesting guy - a biologist who was deported to Mexico after living in the US since childhood without citizenship, and then tried working in a lab in Mexico, but the pay was so bad he learned to code and eventually became a TVC.
Extremely cool individual who I miss. Maybe I should say hi to him.