
1) The White House posted the clip in the first place (dumb on their part but idk who’s saying it doesn't exist) 2) This was in response to the “why now” question, for which he gave two reasons and this was just one. 3) I believe multiple times in the same speech he reiterated that this needed to happen regardless of Israeli action.
In the short term, but long term a regime that doesn't fund terror decreases the risk. Iran has also proven a threat to global trade in both the Suez (through Hezbollah) and Hormuz. It weakens our adversaries, Russia and China, basically booting them from the Middle East entirely. It also helps our allies in Europe by weakening the military support Russia receives from Iran (mostly in the form of drones).
Then there's the benefit of a better regime for the people. Even if the regime is only slightly more moderate, it really can't get worse for them than the previous regime. I'd imagine the new guys won't be gunning down their people by the thousands as much given the president we’ve set.
The only possible way for us to install a new regime would be boots on the ground, which means yet another forever war in the Middle East destroying an entire nation and creating new problems. There is no good end to this we should have just left them alone and let Israel deal with its own consequences for being a geopolitically aggressive genocidal ethnostate
That’s why I said slightly more moderate earlier. You don't need a total change to achieve our goals, just someone who can play ball and isn't actively trying to kill us 24/7. The Venezuela treatment works just fine. And while that wouldn't be a total win for the people, it might at least make things more bearable for them. But if they do rise up like they did in January, we wouldn't need any boots on the ground anyways. At most we'd only need to arm them.