Probably for them, it's not unlike being a professional Star Trek fan. They get to travel around the country and meet people, make some money, and have a few interesting stories to tell. Owning the libs is a bonus.
The Trump Merch Grift Bus is pure carny bullshit. These folks are taking advantage of a popular sales trend and they put too many eggs in one basket, then dropped the basket. 3 years ago, they'd be shilling for bitcoin. 30 years ago, they'd be selling beanie babies. 200 years ago, they'd be selling tulips.
The conman is just the face you put on your bus full of cheap plastic crap sold at 100x markups. And you get to this point because its an ostensibly quick way to turn a few thousand bucks into a few hundred thousand.