This is a behavioral qn:

I would address it from 3 perspectives

a) Impact to # of users- a product/project that would impact large number of customers positively, helping them improve their lives, connect with each other etc.

b) Chance to work with Talented individuals- Chance to work with large number of talented individuals. Learn from them as well as enrich them with my experience

c) Relevance to the company- Projects that are a high priority to the company and highly aligned with the business priorities