Good point. Yet elements of the establishment - such as the aforementioned David Brooks - are moving his way.
I suspect part of that is that the establishment recognizes the desirability (necessity?) of having a Florida pol on the ticket, and Jeb has disappointed so far.
It's also the case that Rubio was absolutely the establishment politician on one of his signature legislative efforts: immigration reform.
As I have pointed out before, this was a bill that establishment icons like McCain supported, and the Dems were willing to accept. It was actually a crappy bill from a lefty perspective - way too punitive and too much border control silliness. Moreover, from a D perspective, it would give the Rs a chance to claim the credit for passing meaningful immigration reform. Which is to say the the Rs were idiots not to jump all over this before the Ds came to their senses.
Of course Rubio has been walking back his support for his bill ever since. Cruz is using it to hurt Rubio in the debates, although Rubio has been holding his own pretty well.