The point about un maintained modules is also true, why are they listed if they are not maintained?
The modules are in general provided by third parties. At some point the enthousiasm for XOOPS or programming in general may fade, due a lot of reasons. That means the original developer doesn't maintain this module anymore.
This doesn't invalidate the quality of these modules. A lot of unmaintained modules are still in use and do everyday a fine job. So, there is no reason to unlist a module, just on the fact it is no longer maintained.
If problems arises and there are still users for the module, I'm sure someone will find a solution and provide a patch or new version. That's all what open source is about!
FYI: We are busy with trying to improve the repository, for having better listings.