I think elgringito has in mind the stereotypical infrequent flier who fires up orbitz or whatever and plugs in his cities/dates and then buys whatever comes up as cheapest. I don't disagree that there are a lot of people who fit this mold.
And that is it. until very recently, you wouldn't find JetBlue or Southwest on these sites. So from what was presented, what would motivate you to choose a more expensive option? Same amount of room, same service, nothing different. So of course you are going to pick the cheapest option.
As for Continental, yes they do offer a meal. I quite frankly did not even know they HAD a real IFE option. Not everyone LIKES the assigned seats, at least you have a CHANCE of getting a good seat on Southwest if you get there early. But that little sandwich, that you can pay $10 for in the airport, is not enough to justify $50-$60 difference in ticket price.