Trump didn't do as much as he could have, but he still permanently damaged both the credibility and survivability of the regime. Assad's victory in Syria ditto. J6 wasn't what it could've been, but it still scared them enough to cripple the military with an 'extremism stand-down' and pull out of the middle-east. Russia-ukraine shattered the myth that the U.S. could protect its puppet-states and punish its enemies effectively, and, as a result, we saw the Saudis disalign from the U.S., and a bunch of other countries get cold feet. 

Things do happen, it's just there's a lot of inertia and institutional power trying to hold things together, and new equilibria start to feel normal after a while. Drastic, immediate changes are rare, even as the result of drastic, immediate actions.