lack of footballing talent maybe, but i wouldn't say he has no heart. he looks to me like he gives 100 percent all the time, but when you're a limited footballer that may not be enough sometimes.
This might be the only time I've seen someone say Simpson gives 100%. The amount of hiding he does from the ball should, on it's own, knock that down to about 25%.
ive rarely seen simpson hide from defensive responsibilities, in the oppositions half, yes he does hide as he often rather loft a ball or whack it away rather than compose himself and pass to a team mate.
Given the fundamental difficulty involved in hiding from both attacking and defensive responsibilites, you're basically giving a well-paid footballer credit for not simply walking off the field of play.