"What about his policies are you seeing as unappealing?"
For healthcare, it is the elimination of the patient's right to choose how they receive healthcare. You get what the government is willing to offer, or get it outside the US. That's a very extreme position to hold, and one that's not been replicated anywhere else. Maybe Canada, depending on who you ask, but certainly nowhere else in the developed world.
And then there is how that healthcare is paid for. Many, many people would pay more, far more even, to have their options removed and replaced by something of a much lower quality. And like I mentioned, it wouldn't be paid for the way Europe does, but he would attempt to shift the burden to higher income earners. Which is a shift proposition, given that you can't collect taxes when people aren't willing to pay it.
Bernie is an old school, unelightened progressive. That plays well with the far left...but between us girls, that's the only area he plays well. As of 2017, 75% of USans considered themselves conservative or moderate, with only 25% calling themselves liberal. Bernie has staked out his territory on the far left...with no room (or even inclination) to shift back towards the center. And it seems very unliekly to me that his polcies are going to appeal to many moderates, given that his policies don't even resonate with a large swath of the Democratic party, inclduing the current front runner.