Senior leadership at enterprises, in my experience, does very little collaboration. The CEO or the board make a choice to install a senior candidate in some senior position. That senior person drags behind them a retinue of trusted aides and associates, whom they busily install everywhere their reach allows. Most of their activity from that point on is trying to demonstrate that their team is the best, shitting on the remnants of whatever came before them, and forging non-aggression pacts with other people of their rank within the enterprise.
We often saw rolling waves of departures after a senior reshuffle, as departing senior execs took "their people" with them. Why stay if the next boss will consider your existence a threat to their ability to cultivate prominence and influence?