Many projects have a BDFL/sole maintainer structure not because that person wants to be in charge, but because there's no one else to share the responsibilities of leadership with. Larger projects with multiple maintainers may also wish to grow their leadership if they feel they need more help.
Signs a project needs more leaders include:
Cultivating leadership requires attracting potential contributors to the project, identifying those who have a long-term interest in the project, developing strong relationships with them, empowering them to believe they could become leaders, helping them build necessary context about how the project works, and helping them find leadership roles.
This is a lot of work, but on the plus side, "helping to cultivate community leaders" is a task that can be at least partially delegated to new community leaders. You can create a virtuous cycle where community members are empowered to empower each other.