What else can he do in it? He's been world champ, now is double Olympic champion, he's got nothing left to prove. He should focus properly on the road and see what he can achieve.
He's said multiple times that MTB is what he enjoys most and wants a crack at DH. If road didn't pay the best I don't think he'd carry on not winning the TDF.
Not to you and maybe not to him, but it certainly does to some poeple. Why do you hope he stops MTB?