As projects grow and change, they may need new governance structures. Perhaps the BDFL wants to step down, and there's no single other person ready to take their place. Maybe the project has grown so big that no one person can make all the decisions. Or a project that people depend on for their lives and livelihoods may want to give users a role in decision-making.
There are many reasons why a governance transition may be necessary. The question is: how do you make that transition in a way that's good for the project? That re-engages people instead of alienating them? And that, ideally, doesn't take up too much of your time and energy?