Michael Brendan Dougherty identifies the main source of enthusiasm for Rubio among Republican elites and pundits:

The other reason that Rubio-mania will take off is less inspiring. Rallying around Rubio will just be too strong a temptation for the GOP’s elite and the most established organs of the conservative movement. Rubio’s candidacy is essentially based on the premise that nothing from the George W. Bush era has to change for the Republican Party.

That’s in line with what I said last month. Rubio’s candidacy represents the conceit that there is nothing so wrong with the GOP or its agenda that can’t be fixed with more wars and more immigration (and more Republican support of both). As I put it then:

If Rubio could win, it would mean that the discredited Bush-era agenda was still viable (among Republicans at least), and it would mean that the people that created and supported that agenda were still in full control of the party. The old rules that say that the party elites’ favored candidate gets the nomination would still be in force. For all the talk that Rubio is a “generational” candidate who would lead the GOP into the future, a large part of Rubio’s appeal to his (relatively few) supporters is that he promises to take the U.S. back to the Bush years: U.S. “leadership” and activism abroad and vaguely “compassionate” conservative activism at home.

However, the upheaval in the Republican primaries this year shows that most Republicans are absolutely not satisfied with keeping the party as it is. Rubio has obviously been the candidate that party leaders prefer to Trump and Cruz, and most Republicans have been very clear over the last year that they want nothing to do with the things their leaders prefer. The more that party leaders try to foist Rubio on a party that is sick of their leadership, the more he will be rejected. The fact remains that the people that haven’t been experiencing Rubiomania are most Republican voters, and most of them aren’t going to because he offers them nothing except a rehash of policies that they know have already failed them.