Engineering vs Product. You can have very exciting engineering behind what is otherwise a very boring product. I'm currently leading a React Native app team and from an engineering perspective, it's very exciting. Bleeding edge everything, fabric, hermes, beta and alpha versions of multiple devtools, etc. From a product perspective it could not be more boring, we're building an app to help insurance salespeople track their sales.

And of course there's always the money, for the right price I'll work on whatever you want me too. If someone offered me a job building Windows Vista widgets for $1M/yr, you can bet I will take the job and be very happy.