It’s not moving from one company to another.
It’s moving from the government regulator to a company regulated by that former employer. The rules on government conflicts of interest still apply, and you can’t accept a paycheck from a regulated entity while you’re still technically employed at the regulator.
I know several people in this category: still employed by the government and subject to government ethics rules, unhireable by any company that still needs to follow that government agency’s rules about conflicts of interest.