Most of Hillary's voters support her reluctantly because they don't want Trump to win. Ask any of them why he's voting for her, and you're very unlikely to get an answer that doesn't mention Donald Trump. I'm sure a lot of them are afraid to come out in support of Hillary, or they're just so bitter about the election that they don't want to be seen having to do anything with it. On the other hand, Trump's supporters are very vocal and have no shame in publicly supporting him. They're as gullible and stupid as a herd of lemmings racing to jump off a cliff (as are the ardent Hillary supporters, I might add), but they do indeed make a lot of noise.
Also, Donald Trump is a huge celebrity outside of the presidential race. Many people (including myself) are just following him for the entertainment value without having any intention to vote for him.