The Sunni states could never have attacked Iran without suffering severe damage themselves. In addition, US policies have brought an immense amount of pain and suffering to the Sunni world itself so the US has hardly acted like a benevolent “ally”. Actually, the US media has spearheaded the demonization of the Muslim world for the past four decades so that has also generated a lot of simmering resentment. Either way, the US has been full of hubris and has followed a destructive policy, China saw the opportunity to shift the global balance of power and took it. This would have never have happened either without the US turn against China. Now that China has nothing to lose, it will work hard against American interests with zero regards to the bilateral relationship unlike in the past, and China has many strings to play as well. It is a country that is spoken softly but carried a big stick for very long, now the world will see more of that big stick.The Chinese peace-pact between Saudi Arabia and Iran has shifted the stragetic map significiantly.
The Americans are the kings of allies and the plan was to sacrifice Iran for Israel, KSA, UAE, Egypt, Turkey and other regional allies. The Americans outside of NATO their strongest alliance is the Sunni-bloc and they are numerous in numbers if you add them on them of NATO it turns into like 80 countries coalition. If the Americans had delivered Iran meaning if they were to storm together Iran this would have only tightened their alliance further and enough to convince them to join them on a Chinese adventure in WW3 because at that point they will have a significiantly large cannon fodder group on top of NATO and land corridors. The Chinese understood that a large coalition was building against Iran which could have potentially splid onto china itself and Iran is tied to Russia and China can't leave Russia and they saw this major stragetic error and allies forming against Iran and in order to separate the allies the Chinese came up with the peace pact in order to divert this massive coalition forming against Iran and eventually and potentially one that could splid over to themselves at later date.
But now the Americans don't have anything to deliver to the regional states as they have mended ties. They have nothing to offer on the table to entice them. Hence why Israel's Ex-Premier minister Lapid said ''Our walls have been teared down'' Because the US and Israel wanted to use them as shield.
These regional states aren't chellengers for the world hegemony themselves but they are swing states and can swing the power balance to one of the 3 players (Russia/China and US) significiantly. The US has put alot of effort into grooming them in order to use them as cannon fodders at later date and the enticing price was suppose to be Iran on a plate but now they have lost that card for good