There's a difference between people who are seeking
temporary work permits, and people who want to move to the USA
permanently. For example, suppose a German engineer wants to work in the USA for two years while setting up a new production system for Bosch in South Carolina. If he gets the visa, it's very specific for two years, and for Bosch work only. After the two years, he has to move back to Germany.
But suppose he changes his mind and wants to move to the USA permanently? That's a different kind of application. If he gets approved, he can move to the USA, and work for whatever company he wants. He will need a green card and residency card for the specific state in which he lives. If he moves to another state, he needs to reapply for new cards.
If he wants to become a USA citizen, then that's an additional process, and that has minimum time requirements, and a test that must be passed.
These are just general explanations. There are more details here:
Services & Benefits