As far as I can tell, Cruz is following election law, and paying attention to the details of each state to maximize his rather slim changes. As a bonus, he is keeping Kasich from rising, which makes it much harder for the establishment to nominate Kasich. Trump would be best off with both Cruz and Kasich out of the race, but that won't happen. If Kasich stays, it's best for Cruz to stay too (I have analyzed a fairly large number of elections, and a three-candidate race is the next best thing to being the only one left). I'll vote for Trump - happily - but I certainly won't condemn Cruz for staying in or for trying for delegates.
The bigger issue is that the GOPe pitching a fit about Trump means in my view that they're not serious about winning the 2016 presidential election, and the future of the Supreme Court that's bound up with it.
The Republican Party could have easily had the presidency wrapped up 4-6 weeks ago, given the total disarray on the Democrat side.
I don't often indulge the whims of children - and the GOPe is acting like children, or something far darker.