It is hard because more people means more opinions.

* Involving the developers in everything that the product team does as well as all of their own work is too inefficient. * Involving the wrong developer means you might not ask the right questions up-front. * Some developers are too negative and block things early on * Some developers are too positive and will say yes to everything even if it is unreasonable * There is not always a clear authority between product owners and developers * A lot of decisions are based on company priorities that might need someone outside of the product/development team to argue for