Did Mordechai really suspect that Esther would do something so low?
hamispalel ba'ad chavero vehoo tzarich leee'oso davar hu nenah techila. There is a power in a tefila that comes from a lev nishbar. A persn who needs something and his heart is broken because of it, and even so he gives away that power of lev nishbar to his friend who also needs the same thing. It is only fitting that he should not lose that power for his own needs and he is answered first.
Mordechai told Esther, don't think you can escape the decree, you are in trouble just as much as everyone else and you are 'tzarich le'oso davar' and that is why your tefila can have the desired effect.
Pachad Yitzchok