They are local Republican activists at the conventions, not big shot "party officials". You'll just have to excuse them for wanting an actual conservative Republican to be the nominee.
BTW, they are picking a nominee for a party. It's not actually the Presidential election yet. Nothing says all the voters have to get a say in who a party chooses to nominate to represent the party in the election. And historically, it wasn't usually done that way.
Historically it has been done that way if you want your ass handed to you in the General. Which seems to be the plan here.
They are thinking it's time to cut Cruz.