Bombing Iran's oil infrastructure would give Iran the casus belli to do a like for like strike on the GCC countries. Imagine strikes on Fujairah port, the Aramco, ADNOC and QatarEnergy refineries on the Gulf Coast, as well as the Yanbu and Habshan pipelines.

That means effectively taking out 25℅ of global oil supply -> oil at 150-200 a barrel -> Trump and the Republicans lose the midterms badly -> Trump gets impeached. I'm sure somebody explained it to him that this is exactly what would get happened, which is why he did not overextend or let Israel do so.