Because that's worked for them so far.
It's not like this is some untested tactic that failed them in the past.
This is a guy who ran on "I'm gonna build a wall and make Mexico pay for it" and then got elected, didn't built the wall, asked his followers to pay for the wall he promised Mexico would pay for, their dumb asses did it, and then he still didn't build the wall.
Again will it work again, will it work long term, all that is highly debatable but there is no way to deny that acting exactly this stupid in exactly this way is what got Trump elected in the first place.
Trump is Don McLean playing a concert. Yeah I'm pretty sure he's gonna play American Pie.