I feel the same way; I have my own plugin listed on it.
The way it works, is that the author of the Plugin Manager has to release the updated list of plugins. It is honestly up to him and his schedule how often he does it. Sometimes it’s a few weeks, other times its several months. I believe part of the issue is that every time the list is updated, it is redownloaded alot since everyone running Notepad++ has to get the new list. This file has to be hosted somewhere, and since it is downloaded so much, not many services want to host it for free. I would strongly agree that it is very important to make sure those lists are refreshed as often as possible. I think I recall he posted on the forum a little while back he is looking into working with some service to host the updated list for him, but not sure how much that has progressed. This list has been downloaded over 77million times this year alone. There is also an md5sum that the plugin manager downloads first to see if the list has been updated. This file has been downloaded over 198million times this year. So it is easy to see the bandwidth really adds up, even with small file sizes
Side note: I’ve seen alot of other “plugin managers” for other software (e.g. games, etc) host the list on Github, which I think is a beautiful idea. Just simply create a pull request to add your plugin’s information to the list. But again this goes back to the issue of this single file being downloaded so much. :(