Two reasons.
One it was off the record.
Two they will still release it after Trump gets the nomination. They want Hillary to win and best chance for her is for Trump to win the GOP nomination. Regardless if you agree with that or not that IS what the liberals think. They want Trump to win. Of course we thought Obama would be easy to beat as well.
Easy enough to prove Cruz and everyone wrong. Trump just needs to tell the NY Times to release it. He has nothing to fear since I’m sure he didn’t say anything other than making the wall bigger and better.