3 points
1) There are no paid operatives to run interference when the candidate has destroyed his candidacy by his lonesome. Numbers were trending down months before the Trump surge began.
2) Nearly all the people who find Trump palatable in this sea of mediocrity are driven by anti-establishment motivations. In other words, smash the beltway triumvirate of think tanks, lobbying groups and politicians. Logically, there are little to no coattails for Cruz or others, since they are viewed as part of the problem.
3) The Rand cultists live in a self-enclosed bubble in which Rand is secretly leading but is being held down by the media and the malcontents who jumped to Trump.