Why Are So Many People Running For President?

Running for president is expensive and exhausting — but this year, some 22 people seem to think it's a good idea. There are five major candidates for the Democratic nomination and a whopping 17 on the Republican side.

But why? As it turns out, there are many reasons.
http://www.npr.org/sections/itsallpolitics/2015/09/05/437699700/why-are-23-people-running-for-president