I cannot imagine where they thought this uprising was supposed to come from. Plenty of Iranians are unhappy about the current regime, but that doesn't mean they've got a new one prepared to replace it.
Even in Iraq and Afghanistan we started with at least a rough idea of what followed a regime change. In both cases it was corrupt and ill thought out, but at least it existed.
Perhaps telling them you'd help and then rug pulling had a long-term effect?
(Trump said this in a post on his social media site)