They’d like Trump gone, but they’ll be just as happy if they can divide the base into 4 quadrants of Fiorina-Carson-Yeb!- Trump so that Yeb! Will win with 21% of the primary vote.
And the only ones who can make that happen are the supporters of Fiorina and Carson. At some point, as they see the scenario developing, those supporters need to throw in with Trump, as the supporters and moneyed interests of Bush will not (too invested). I am of course assuming that Trump's large numbers hold.