Because they don't want him to be? He's much better now at Madrid, than he was at United. Benzema is a team player, because he knows that someone else can score goals better than he can, nothing else. He's sorta like a F9 at Madrid, allowing the IFs to come upfront. Isco needs to be a teamplayer, it's his role. He's there to provide assists. Their roles determine the teamplay. Ronaldo is their best finisher, so it's pretty obvious he'll take more shots.
never thought of it that way, i just prefer the team players than the individual players (if you get what i mean)