Yes, yes , yes, we all know here what a disappointment Rubio is as a Senator. But to the great average voter, only barely aware of political nuance, he is a conservative former Florida house speaker who gave a conservative speech at the convention a few years back and is now ending his first term in the Senate.
In their minds, he is conservative and not establishment. All the old establishment types and establishment governors went down with less than 25% between them.
You can put lipstick on a pig and it is still a pig.