Although I agree that GF2 is a great movie (although, IMHO, not as great as its predecessor), if I were Coppola I wouldn't have made it, I'd have stopped after the first one. After having made such a great movie I wouldn't have wanted to risk a sequel tarnishing it, since sequels are almost always inferior to the original. And "The Godfather" tells a complete, self-contained story by itself, it doesn't need a sequel. Coppola was really lucky the second one turned out as well as it did (obviously, his luck ran out with the third).
Well as I'm sure you know FFC was a bit miffed that GF1 wound up (in some circles) being interpreted or understood as a love letter to or romantification of the Mafia and wanted to tell a story that made it virtually impossible for anyone to miss the point that these were bad people. He was also quite interested in showing the bad side of capitalism and used the Mafia as a metaphor. I don't know if he still feels that way now but those were his feelings in the early seventies.