I'm guessing Trump is not pushing the Iranian regime for a deal because he believes an internal civil war is more likely if we aren't bombing the crap out of them. Being actively attacked tends to paper over differences, whereas economic warfare (the blockade) might exacerbate internal differences.
This of course raises questions. First, is a civil war possible given the IRGC has most of the guns? Second, will life get bad enough fast enough for enough Iranians to shift the national center of gravity? And third, what proportion of the IRGC aren't martyrdom-seeking fanatics but signed on as a smart career move and are faking to-the-death commitment. I don't know those answers, I'm not certain anybody knows.
I do know the conventional wisdom is that regime change requires boots on the ground. Trump seems to be betting that's no longer true, we'll see what happens.