Why did Formula 1 need Audi so much that it was prepared to use 1.6l 4 cylinder engines to get them in?

F1 wants more engine manufacturers to give the field more options to choose from and to progress the Sport. Also most engine manufactures have a limit on how many teams they provide engines to. Lastly it wasn't just Audi, Renault wanted 4 cylinder engines to as more closely aligns with their road cars, they even threatened to back out of the sport if 4 cylinders wasn't agreed on.