There are a significant number of Republican who don't like Trump and who either don't like Cruz or think he is unelectable. The problem for many of those voters is that no consensus alternative had emerged. So, many of them were still undecided, or were splintered among other candidates.
When Rubio moved into third place with 15%, he became the obvious non-Cruz/Trump alternative. A solid debate performance helped as well. So all those people who were looking for an alternative gravitated to him late, and so his numbers went way up.
Entry polls showed that Rubio did very well among those who decided late, and particularly among those who prioritized winning the general election.
Now, maybe you think that's a dumb reason to vote for someone in the primary, but a lot of folks disagree. I've got family members on the East Coast who leaned Christie, but are now switching to Rubio because they think he has a better chance of beating Trump/Cruz, and winning the general.
All completely rational, no conspiracy or cheating required.
Your premise is well put forth and thank you for it. I still think that the deplorable sinking of the media to the depths of becoming political shills spells doom for our electoral process. So does the practice of introducing “market science” to something so important.
The debate farce that has become so popular with Americans amounts to nothing more than cage matches. They actually reveal very little about the character and policy stances of the candidates.
We have become the stuff of fiction novels and tabloids in real time. It’s sad that the majority of Americans have known nothing else.
Surely you will agree that we no longer have two diverse political parties but what amounts to uniparty. That was evident after the last election.