Because he has none to offer. He's promising without thinking yet again.
If we heard the details of his plan we would reject it. More hope and change...
Trump: "I have a heart. I want people taken care of. If people have no money. We have to help people. But that doesn't mean single payer. It means we have to help people. If somebody has no money and they're lying in the middle of the street and they're dying, I'm going to take care of that person," Trump said on ABC's 'This Week'. ... As he did in the "60 Minutes" interview, Trump said his plan would be to work with hospitals and doctors to set up a better system. And then Trump took another dig at Cruz. "I mean, maybe he's got no heart. And if this means I lose an election, that's fine, because, frankly, we have to take care of the people in our country. We can't let them die on the sidewalks of New York or the sidewalks of Iowa or anywhere else," Trump said.
http://www.cnn.com/2016/01/31/politics/donald-trump-ted-cruz-health-care-obamacare/index.html
Not true. Trump said it would be "something terrific". That's enough details for the Trump supporters.