And you never know who might want to take over or what kind of great new enhancements someone else might contribute that make you proud that you started the project to begin with. Even if the code languishes on github or sourceforge at least there's the possibility for someone to pick it up. What's more, you never know who's picking up abandoned projects and using them privately. Just because there's no cmaintainer or community activity that doesn't mean there isn't the odd person here and there who finds an abandoned project and uses the hell out of it. Contributions from the open source community isn't the only measure of a project's success or usefulness. Individuals finding a use for abandoned projects without contributing back is still a great thing in my book.
I don't know about everyone else but I do it for the love of the game, not to see my name in the source code of another project that uses my code. As far as I'm concerned, unless I'm planning to make a profit (in which case I wouldn't publish the source), you can fork, close, distribute and charge whatever you want with my code.
I like Alex's style on this one a lot.