I think that busy musicians possibly are the ones that just haven't had many opportunities to play with other musicians. They sometimes are used to being the "whole band" and have little concept of team playing, because it IS two entirely different things.
That being said, as a primary keyboardist, but also a bassist(secondary) and a drummer(when asked), I tend to be very mindful of the musicians around me because we do have to work together. As a bassist especially, I cannot stand to have a busy keyboardist, who TAKES OVER my role on the bottom end, and there are times I will just put my bass down, and let them have the whole thing. I don't know, maybe I just think differently because I do play other instruments as well. I have a "Band sound" mindset.