Why do Democrats label themselves Progressive?

[Napoleon]

In America, progressivism is liberalism and liberalism is progressivism. What I mean is that we associate the term liberal with more left-wing economics like welfare programs and union support and the term progressive is associated more with socially liberal positions such as environmental protection and gay rights. Someone like me who would (maybe) be a social-liberal would be referred to as a Progressive. Liberalism tends to be used to describe left-wing populism.

[Napoleon]

I like the change to progressive.  Real freedom lovers should take "liberal" back since no one is using it anymore.

But then genuine libertarians like Dennis Miller, Glenn Beck and Wayne Allen Root couldn't call themselves that anymore.

I'm not a fan of libertarians, but that is just insulting to them.

I don't think any libertarian that wasn't a rightist hack would consider any one of the three remotely libertarian. They are pretty much all sugar-coated conservatives who reject any kind of safety network and therefore have to rebuke GWB-style conservatism in favor of a new name.