Will's been focused more on movies in the last couple of years. He's not only a recording artist anymore, so it's likely that he doesn't have time to do movies, do his own music, spend time with his family, stay involved with Overbrook, do charities, and still record remixes for people.
Also, though he should, Will doesn't have the respect in hip hop that others have, so people wouldn't necessarily call him up to do a remix on their song.