My initial motivation for my (small) projects was always to scratch my own itch. Beyond that, it feels really good when someone else uses the code. For my current side-project, I keep up maintenance because it's interesting work and because I can plausibly benefit from bug fixes. It's neat to see how other people adapt the code and open up new use-cases. For that reason, I love high-quality bug reports and treat them with some urgency.

For projects I lose interest in, I unsubscribe from everything and either mark the project as maintenance mode or try to find a maintainer. To find maintainers, I've had good success granting write access to anyone who lands a few good PRs and telling them they have free reign over the code.