Not to detract from your argument at all, but IAH-LAX is the largest non-hub route by passenger volume for CO, so it is not just a regular destination. EWR-MCO was next in the stats I saw.

The fact is that CO doesn't have wide-bodies to run domestic routes, and if they did have them they wouldn't use them on domestic routes. The real money is on international routes and that's what CO is going for.