Because they already have it under good enough control. Your question is like asking why the US does not invade Texas and take their oil.

They don't pay us anything to sell their oil. We have a relatively small partnership with them, but that's about it. And they're part of OPEC, which is deliberately designed counter to US interests.

because saudi already pays them. Saudi is already in their control. Iran isnt so they are plotting a regime change there too, use your brain.