Suppose it would cost them X million dollars a year to provide the feature and providing it would cost them nothing in terms of sales, and indeed get them a few more because people like the feature. Well, it still costs them that amount to provide it, so then the question is whether X is less than Y. But you don't control how much it costs them to implement it, only how much of your business you're going to take somewhere else without it, and if nobody is willing to do that then why would you expect them to spend the money?
It doesn't have to be that they're purposely screwing you. It's just that if you don't care enough to choose differently then why would they?
