Carter doesn't pound nails for anyone but himself. The reason he is in to Habitat is because it keeps him relevent- it keeps his name in the news. Without that and a timely crisis he couldn't surface every once in a while and get a hearing in the press to put out pink bull-excrement- he would just be ignored or forgotten.
It's like Clinton- who can't bear to be forgotten because if he is, he wouldn't get freebies, givfts, or girls, or be able to stroll into restaurants and get preferred seating... and nobody would foot the bill.
Don't think anything they do is out of the goodness of their hearts.