He chooses to not be involved at all, so how is he ever going to make a difference.
Grimm has said many times that during his run as the main creative force behind Smackdown, the shows viewing figures were up, so being hamstrung by WWE control wasnt an issue.
And as for TNA, you only have to see how much control has been ceded to Hogan and Bisch to see that it wouldnt be impossible for Heyman to be given full control, or at least be able to gain a strong hold on the creative side.
Fact is, he isnt interested anymore, and would only go back if he got everything he wanted, and thats not good for the business either, because nobody knows if Heyman 2010 would work.