His agent is taking care of his own pocket, like every agent is doing nowadays (just look at Ronaldo).
The thing is:
a) Sporting has made a clear bet on recapturing the title.
b) The release clause is no longer active.
c) Sporting has made a financial effort to keep the best players and are prepared to take it until January, according to CL career will be.
d) Moutinho never came out saying "I wanna leave and that's period!"
e) Moutinho is the best paid player in the squad.
f) Unlike Veloso, who stated that he wanted to leave if a club of the next level would come along, Moutinho never said nothing as defining as that.
g) With all honesty I don't rate Everton as being any step higher than Sporting (Sporting plays to win things, will play in the CL against Europe top dogs, has great support, great working conditions and facilities almost unparaleled in the World)
h) ....
So there are a lot of things that make this deal a hard one to do. At least at this point of the season. Which is pretty silly because if Everton reach 25M€ mark they should have done a month ago while the release clause was active.