Nah, I think "entitled" is the right word, but maybe not exactly as you used it.

There are "amateur" competitions in many disciplines that are only open to people below a certain threshold of skill, for the enjoyment of the regular Joes who have other things to do besides get really good at that discipline (it's important to note that while it's common to bar people of exceptional skill from competing, it's extremely rare to bar people of exceptional free time from competing, but for the purposes of this argument we can assume considerable overlap between the two).

The problem is, that isn't what this competition was. 343i + sponsors decided to give away a truck to the best performer. When you (not you, trappe, the others) say "it's not fair because I couldn't play enough to perform well" you're implying that 343i owed you an equal shot at the truck. They didn't. They wanted to give it to the best performer, not to the best performer considering each individual's circumstance. To suggest they owed you this fair shot you didn't get is entitlement.