We want to be green so we're trying to stop drilling for oil. But we also need oil because our society runs on it. This guy has oil. This guy can therefore do whatever he likes. This is obviously way better than drilling at home.
There's lots of guys who had oil who, when they did things the US didn't like, found themselves without anyone to sell oil to, without a country to run or maybe worse.
I agree KSA has a special relationship with the US (and much of the west), but it's not just about oil.