As title asks, why do you think men are so resistant towards commitment?

As a man I believe part of the problem is that being in a relationship is a great burden for a man and it takes a woman with a lot to offer to offset that. I say it's a great burden for a man because even tho women experience similar difficulies, I'd say men still hold most of the burden of performance, and would otherwise enjoy casual sex more (studies say casual sex is more enjoyable if you're a man). I'd like to hear other opinions on the matter.