While I agree with the "result of a public teeming with frustration over status quo politics" part, and that was a big part of it, the fact that it was Trump being the messenger was and still is a huge problem for many in the party that wanted an outsider.  (And again, it wasn't just people in the party alone that made Trump the nominee, thanks to stupid open primaries.)

Well less than 50% of the party wanted Trump as the nominee.  But they wanted right-wing Cruz even less.  And all the mainstream moderates had cancelled themselves out by then.  At that point voters had no choice for the nomination, although many were still hoping for some way to replace Trump as the nominee.  

And of course when faced with Trump vs Hillary in Nov, the vast majority of the party is obviously going to choose bad over worse.