Why is the establishment lining up behind Cruz?
Because he is one of them. They want to keep their power and their perks.
Because they can make deals with Trump!, they said so earlier in the campaign. Cruz has stonewalled them and fought with them to get them to toe the line in the Senate. No deals there.
They finally realize they can do more to scuttle Cruz with an endorsement than an attack, which would be taken as a reason to vote for Ted.
Because they see the writing on the wall. If they do a contested/brokered convention.....they loose a good part of their base.
Rubio/Kasich CANNOT win the nomination. The anger against the party is too great.
Trump is too far out there to connect with Rubio/Kasich voters. Cruz is "milder" and could win them over....and no matter what Trump supporters like to think, Cruz can win the "anger votes" because he IS part of the early revolt against the GOPe. He's been fighting them for years....while Trump was still supporting Democrats.
They know Cruz will loose to Hillary and they would rather have Hillary than Cruz.
They aren't. They hate him. He is not their "Judas horse", Marco is. (Now that Jeb's out.) The GOP-E totally hate Cruz, esp. after he directed some National Republican Senatorial Campaign (NRSC) funds two-three years ago to Tea Party challengers of old GOP-E bulls, one of whom was Mitch McConnell himself. The Old Guard totally flamed Cruz.
They LOOOOAAAATTTHHHHHE Cruz.
In fact, just guessing (and Rush Limbaugh put this up, too), the current GOP-E leaders would rather try to do a "deal" with The Donald. He's made it tough for them, but dealing with Ted Cruz is a total DOA non-starter.
Heidi's CFR work is a totally different kettle of fish, and I've seen nothing tying her old man to an endorsement of any NAU nonsense, esp. after voters spanked Dubya on that subject 10 years ago.