Vito liked to, in a sense, drag things out. For example, he could have told Bonasera yes or no. But he enjoyed maneuvering people into a position of dependence, supplication, or misapprehension. he also could have told Sollozz yes or no over the phone or by messenger or whatever. But he enjoyed the joust, the performance.
That aspect of Vito's character is superbly portrayed in II, in his scenes with Sr. Roberto. They're among the best in the Trilogy.