Good point, they don't know about the reforms. I went and reread recent chapters and it seems the reason is more simple, they envy him. A, from their knowledge, Commoner suddenly turns up, does "miraculous" feats (Some don't actually believe the stuff Yosuke does INFRONT of many people and think it's tricks) gains the affection of the Princess, the ear of the King, Land, his own Squad and other things. They want it and for the crime of trying to usurp them they want him to lose everything.
That seems to be all really, simple pettiness. And going by the "intelligence" they have shown there is a good chance they only realise how they fucked up once they are about to be hang like the guy that employed Rashanasha.