Saudi and Iran are mortal enemies tbh. So are Israel and Iran
I think US just doesn't see the threat from Iran like Israel/Saudi view it. Iran has a pretty mediocre army. Their generals are getting slaughtered in Syria as we speak. Iran is a joke basically and US knows it. Israel/Saudi make it seem Iran is almighty just because they are extremists states that crave for power.
Also, Israel has nothing to fear, they have a mighty powerful army. On the other hand Saudi has a laughable army, they are probably geniunely scared

their expensive army is currently getting knowere vs people carrying sticks and stones in Yemen