In Godfather III it turns out, at the end, that the one secretly scheming against Michael is (and apparently, always has been) the aged Don Altobello, who by his own account only wants to retire and grow his peppers and tomatoes. OK, so he’s lying, he’s still scheming for still greater money and power. Only – what’s his angle? What would he gain by having Michael whacked?
Only two Godfather movies were ever made.
I think you answered your own question: More money and power.