This is not a very charitable explanation, it takes politicians at their word during a war. (One should not do that, and you can refer to Putin’s language at 2022 as a parallel example to Trump’s)
The initial US goals clearly were: 1. Regime change 2. Denial is of nuclear weapons
It’s also clear these goals were not achieved. So the US changed tactics and goals. (Same as Russia no longer plans on capturing Kiev it seems)
Most likely the US is stalling for time due to oil markets and has the same intentions as before, limited only by current capability.
According to The Economist, the Iranian theocracy is no longer in power, the IRGC is. Still, not the regime change Trump was hoping for, that's for sure.
> Khamenei’s killing has accelerated Iran’s transition from a theocracy to an ambitious nationalistic state dominated by military men. The irgc appears to wield power with few constraints. Clerics who challenged its influence—including former Presidents Mohammad Khatami and Hassan Rouhani—were conspicuously absent from the [funeral] processions.
https://www.economist.com/interactive/middle-east-and-africa...
I think regime change is likely to happen within two years. Just not in Iran.