Its Economic gain. Its not religion or the hunt for more land like the old British, French and Portuguese empires.
Capitalism requires new markets and occupation is too costly and so they turn to economic long distance occupation. The old british empire style of conquest is more costly than beneficial. Now the states can exploit economies with the use of minimum war... war that is just enough to maintain their monopoly over Arab Markets. Thats your world economy.
The gulf countries, particularly Saudi Arabia, are economically conquered by the US. The US will support whoever it needs to support to maintain the blood sucking process.
If the US-Israeli relation were to become less economically beneficial than the termination of it.. USA would forget about Israel and switch sides in a second.