Because people are stupid ... they support the components of the ACA, but dislike "Obamacare". So I say congratulations to the GOP messaging machine.
If the ACA is still in place in two years, it's going nowhere.
and Yank pointed out, the polling does NOT reflect support for repeal but for reforms.
The Democratic messaging machine is what made people believe that Obamacare was some sort of unicorn reform without faults. As they've become aware of the provisions, they don't like it. They want the unicorn they were promised.