When the paint closes down, IT has to look for open shooters more often as he heads to the rim, so teams don't collapse on him so much. If he made them pay more often, the paint would re-open for him. Lately it's like all teams are playing him to score only.
I know his effort doesn't show in the stats consistently, but you gotta love the way Marcus plays, he is annoying players into reacting to him, and forgetting about the team game.