We didn't show faith in him out of some act of charity, if we thought we weren't going to benefit from him in the long run we'd have kicked him out with zero thought of loyalty or disrespect.
He paid us back for our "loyalty" with three excellent seasons (I'm not sure why you think he only started playing well 18 months ago). He contributed massively to our 12/13 PL win, was the only player to even resemble a United player under Moyes and, most importantly, he almost single handedly kept us in top four contention for large chunks of the season. He doesn't owe us anything at this stage.
It would be nice if he signed a new contract and let us make more money off him but why on earth would you expect him prioritize us over his own career?