But, is it just me or has it become rarer for open source project maintainers to feel free to let projects go? I don't mean to let them die, I mean, to find like-minded individuals to which you can defer some or all of the work? I realize that as the original author one feels a sense of ownership, but if you want it to continue, and you don't have the time, there is nothing wrong with putting out a call for someone to take over maintainership.
Most projects that I've maintained have been my own work but I've also taken over maintainership from someone on a popular project, and it was a great experience. I got to work with a good code base, add my own ideas, offer some direction, and I learned a lot about maintaining code for longevity, integrating community contributions, and I cared about it probably more than I have for much of my own work, because I felt that I owed it to the original author to do a good job.
Now, several years later, I do not use it myself as much, and I am perfectly ready to find a new maintainer for it, should someone appropriate come along. (That hasn't happened but the project no longer takes a lot of my time. since new solutions have come along, so it's fine. If it did take more time, it would mean there were more users, and therefore probably there would be more interested parties in taking over maintainership.)
I encourage authors and maintainers who are feeling they are reaching this burnout stage to feel more comfortable putting out requests for help, it can be a good experience and even encourage community building around your work. You don't have to be a BDFL, you can be a temporary one.