Reasons I've been told include:
- A "fuck you" to the establishment and orthodoxy.
- A belief that Hillary is corrupt.
- Entertainment value. One Trump voter I know also donated to Hillary in order to get the "Woman Card": https://shop.hillaryclinton.com/products/the-woman-card
- A support for nationalism and economic populism.
- A belief that Trump can do for the country what he did for Wolman skating rink: http://www.bloomberg.com/politics/features/2015-09-29/a-1980... (I think Peter Thiel falls into this category.)
I know it's tempting to level the worst insult you can think of - raaaciiiissstt - against anyone who disagrees with you. Consider the possibility that this is what allowed Trump to win in the first place.