As near as I can tell, the RNC's only delegate apportionment rule is "The State delegations must follow the rules of their state GOP."
So, the Utah GOP rules say that if only one candidate survives, he gets all their delegates. Simple as that.
There was a minor bruhaha with Alaska and DC. Same state rule, so the same result.
Note that neither the Trump campaign nor the RNC wrote that rule. Those delegates must follow their state party rules for delegates.
It's why some states are "winner take all" some are proportional, and some are a modified proportional rule. The state party decides the rule.
I am fine with why it happened, but if you are going to publish an article about it, explain the WHY.. even in this article it didn’t spell out that the reason this happened was the state rules said they had to.