“What’s in it for me?” is unidirectional. It exclusively spotlights your wants and needs without considering what drives the people and organizations you work with. It implies that only your incentives are relevant — though this is seldom true.
“What’s in it for us?” is multidirectional. It spotlights everyone’s wants and needs and makes it possible to look for mutual incentives. It acknowledges that everyone’s incentives must be acknowledged in order for there to be a good partnership.
Misaligned incentives is a major risk in any operation. If you want to be able to manage them, you first need to ask: “what’s in it for us?”
Focus on the overlap. The more of it you can point to, the more fruitful the partnership will be.