It's more China overpromising and not delivering on the big investments. Whose fault is it that nothing has happened? Is there any evidence that Iranian authorities have been delaying a Chinese project?
It's a major strength of the west that they are strong in choosing sides and that all the western countries are aligned. That's why China has been trying to promote EU independence from the US. But currently they're all working together, sometimes more, sometimes less, but they all feel they're on the same side.
Non western powers aren't very united. Everyone is happy to work with China, but few want to ally with China, because China won't choose their side in a conflict with the west as trade with the west is still too important. If you reward countries with leverage, that always play the superpowers against each other, you can't build your own bloc. So if China actually supports the UAE, which is not very pro China, against Iran, which is almost completely aligned with Chinese interests, in a territorial dispute, what message does that send to other countries that want to work with China? If I were in Cambodia now, I'd be worried about China supporting Vietnamese claims because Vietnam is bigger and has more leverage
For better or worse (it confers both benefits and negatives), US bloc is organized as an union of states that are only in name independent. If a few of them break off, it can easily cause a domino effect.
Iran would be more than happy to join China's bloc, its China itself that doesn't want to pick sides in the middle east when there are so many unresolved conflicts, because it would lock them out of potentially better deals.
The more conflicts can be resolved between the Israel - Syria - Iraq - Saudi - Iran sector, the larger and more powerful the alliance China can reap in the end will be.
The fault of Iran is not in breaking any deals, they're a stable oil/resource supplier. The problem is that due to backwards laws, they will not be able to become more than that.
How many Chinese or Russian academics would go to Iran to create cooperation? Consider many of them are female themselves and/or are going to bring their whole family over for years. Is the political climate of Iran conductive to allowing civil exchange?
By taking the fight against America you lose access to the world's 2nd largest economy and 2nd largest source of scientific publications as well. That is no small loss, but if you also have frankly irrational laws that will end up alienating the no 1 economy and no 1 country in research at the same time, then you created a devastating situation of your own making.
China spent a decade or so curing radical Islam after radical Islam killed hundreds in terror attacks and repressed hundreds of thousands individuals through backwards laws, it is not going to want to have close connections with countries where radical Islam is written in their constitution.