The primary season, for most, is an opportunity to fund raise, and then use that money as a slush fund, so they can live a five star life style as they travel the country. Afterwards, they get the title. "former presidential candidate", and can use that resume booster to get jobs working in the media as an analyst. CNN, for example, will hire anyone who is negative on Trump.
Trump was different in the 2016 primaries, in that he used his own money in the primaries. He already had a five star life style and a good job as CEO of an business empire. He was going for the job of president. This was a life goal, having prepared for that moment in time for over twenty years. He was ready to rumble. This caught the vain and self serving, off guard.
If you remember in the 2016 primary season, Trump was initially treated with kid gloves by the other candidates, becauseTrump was part of the donor class. All the rest of the candidates wanted to keep that fund raiser option open, since nobody expected Trump to go very far. This easy start allowed Trump to get his feet wet, and then he get some traction. After that nobody could stop his momentum, since he was a man on a mission with the eye of the Tiger.