The Iranian regime does have some support, but it's only about 20% of the population. Most of the 80% would gladly see the back of the mullahs, but when they took to the streets two months ago to try and achieve just that, the regime slaughtered them in their tens of thousands. By their actions, the regime showed that there can be no peaceful revolution in Iran. The only way the Iranians will ever see the back of the theocracy is violently.
Nothing would give me greater pleasure at the moment than the Iranians overthrowing the regime, but I don't see how this happens. The problem for the opposition is the same now as it was two months ago. They have no weapons, while the regime and its supporters do, and have shown that they won't hesitate to use them. How are ordinary Iranians supposed to get rid of the regime in those circumstances?
The only way it could happen is if the Iranian army switches sides and decides to take on the IRGC. The problem here is that there's no sign of that happening, and the IRGC is probably more capable than the Iranian army in any case.
The upshot of all this is that it's in the interests of Praetorian Prefects to appoint puppet emperors. Whoever ends up running the IRGC will keep arranging for puppet Supreme Leaders to be appointed, whilst running things themselves as a military dictatorship.