We are at the point in the campaign where everyone decides that the nomination is going to the guy in front of the pack, and there is no need to antagonize that person who is going to be a big shot-caller in the party, so they drop out. Except they aren't.
Trump isn't for obvious reasons. He is going to be the nominee.
Cruz isn't because he is going to win Texas and if only Rubio would drop out, he'd have a clear shot at beating Trump. (Perhaps at the convention < - Best Case Scenario) Yes... I do think Cruz is narcissistic enough to blow up the GOP convention. It is the only thing I like about him.
Rubio isn't because if only Cruz would drop out, he'd have a clear shot at Trump and although the primary voters don't like him, the billionaires who propped up Jeb! do.
Kasich isn't because he is now running for the VP spot.
Carson isn't because all these books aren't going to sell themselves.
The revised standings will be revised in about 200 days when we get to the convention: