1) The new project was massively less interesting to me than the one I was solving (a completely different field with skills I didn’t possess - think moving from hardcore low level system scalability to designing a new type of UI widget, for example), and I tried to make that as clear as possible without undermining management or jeopardizing my job safety.

2) The project was just 80% completed, whereas I like bringing things to production myself, and handle all the maintenance and support. Especially the things that I design and lead from scratch.