Trump had the same opportunity to "steal" these delegates, too. However, he and his staff apparently weren't familiar with the rules governing the now orphaned Rubio delegates. And, as a consequence, they lost out to Cruz's operatives -- who were up-to-speed and capitalized on their knowledge.
I'd say that credit attaches to the Cruz team...while the Trump teamm has some work to do.
Trump had over 4,000 votes more then Cruz and he should have more delegates-period.