My theory: The Bush-Koch-Goldman Sachs Establishment offered him a TON of money to hold out in Trump & try to humiliate him. He’s probably a very rich man now, but his political career is over. He probably can’t even win re-election in TX now. He took to money and ran...as did his buddies Levin & Beck.
Sounds plausible. The Bush-Rove wing of the GOP knew that as runner-up, Cruz was guaranteed a keynote speaker slot at the convention (any winner who doesn't allow the runner-up to do so is perceived as a "sore winner"), so they used him as a tool to humiliate and derail Trump.
Ironic that Cruz whines about not wanting to be Trump's "puppy dog," when he's all too eager to be the GOP establishment's attack dog against Trump. Hope they payed him well, since as you said his political career is now over, unless Ted wants to join Hillary's campaign and reinvent himself as a born-again Liberal.
A Texas poll conducted about 3 weeks showed Cruz at 43%.
He poll numbers will drop even further.
And that will encourage primary competition.