I honestly also have no idea why Iran's economy is so weak. I can only attribute it to that we maybe underestimated the power and the effects of Western sanctions after seeing how greatly they backfired on China and Russia recently and how they dusted them off. However, maybe they really have great harmful potency against these regional powers and 'normal' countries. It is not just Iran, look at Venezuela for example.
These kinds of countries are already not particularly prosperous even before sanctions as part of the Global South, not to mention with such sanctions. The greatest problem of sanctions is their secondary nature that literally no one wants to have much to deal with you to not offend the US, and if you are not internally self-sufficient enough and externally influential, as Russia as of recent, and China, you are kinda done for.
Generally, an autocratic regime like the Iranian (no matter its nature, if it is theocratic or secular) should have theoretically been the most effective solution for their economy, look at what Putin did for Russia for example, or CCP for China. So, I was always surprised why their economy is so shit. So something has to be missing.
It could be true that they spend too much resources and focus on religious matters. But keep in mind that what can keep such a population of a dozen ethnic groups, with Persians barely 51%, united in one place? You guessed it. It is religion. I think that they simply have to invest so much energy precisely because of that, having a trade-off.
Also, basically, some kind of religious propaganda, heavy enforcement, and a strong hand are also necessary once again to keep everything from falling apart. They are not like China which has a strong natural cultural tendency toward centralization and collectivism organically.
