Be ause he promised to do the ACA ONE BETTER, "cover everyone, for less".
And what did he do?
He let Ryan and his assholes co e up with a plan that had nothing to do with what he promised. So, he went on a crusade that "the ACA is a disaster", and lied in many different ways, willingly in the end be ause by now he knew that he had lied.
If he was going to do what he PROMISED, he should have said "let's vote on fixing the ACA, and if that fails let's sit down over tne next year and come up with a good replacement that will do WHAT I PROMISED!"
That is what a PRESIDENT does.