The scuttlebutt is - and has been - that Trump is an outsider. Not part of the GOP-e. And as such, there will be back room deals and dirty tricks played to keep Trump from being the nominee. Even IF he reaches that 1,237 number.
If I'm not mistaken, he could get more votes on a second ballot. It makes more sense that a few would go to the candidate with many, rather than many would go to some candidate with few.
They don't have unlimited time to decide, either. And the crowd outside will be very irritated if the guy with the popular vote advantage gets the shaft. Not to mention the disaffected voters who won't pull the lever. I don't see the benefit in the risk-benefit analysis.