I'll give you the point that we aren't putting as much pressure as we could, but at the moment, do you really think it would be a good idea to invade another dictatorship? While our armed forces could probably deal, I don't think they honestly should have to.
And as to Saudi Arabia: We can't feasibly invade there. People bitch about how we are giving a reason for them to commit acts against us, how do you think it would be viewed if we invaded the holiest of all places in Islamic faith? Hell, isn't it against Islamic law to let nonbelievers even ENTER Mecca? The only way we can change SA is to put political and cultural pressure by changing the surrounding Muslim world. Asking us why we don't invade there is just a strawman.
I'd give Uzbekistan as a better example, the human rights record there has been criticised but money is still being given to them because of there strategic location