I suppose the difference is that the Saudis are too decadent to be aggressive, whereas the Iranians aren’t.
The official Saudi policies are not anti-American. The official Iranians are and they use proxies to attack us and our allies. Many wealthy Saudi citizens do not support the position of their government. The citizens of Iran were, about 8 years ago, pro-American. Saudi is not building a bomb to hit Israel. It’s a big difference.