Are National Guard units not under control of the governors of their states?
Yes, on a day-to-day basis. However, the President can “Federalize” them with a stroke of a pen.
Only when the feds don't have a use for them. The National Guard is officially a reserve component of the US Army. The feds supply all the equipment, arms, vehicles, etc. The feds pay the NG troops when on training. The officers hold US Army reserve commissions, and the US Army completely controls whether they are promoted.
A state can have a separate State Guard, like Texas does, but the state then has to pay all the bills for that State Guard.