We're not. That's why we're bombing the regime and associated military targets. Iran was never expected to give up quietly.
They aren't going to just give up after a few weeks of bombing.
Will need boots on the ground versus a resistance/multiple sides of a civil war, and now we have another 20 year war.
People don't just shrug and go "all shucks, yuck yuck, guess you got us, i'll roll over"