This might sound counterintuitive for a server that wants to have as much variety as possible. However, there is no functional reason to have maps that take up space and do not get played at all. It makes it easier to navigate the map repository as well as ensure that maps, if updated in large quantities simutaneously, don't miss out any updates. It also makes it easier to learn maps that are more consistently played. For instance, there is a certain KoTH map that went 3 years without a match even being played despite being loaded. Maybe even allow for less confusion on which map is what.
Bottom line up front: Easier traversibility, quicker indexing, more efficient for downloading, makes it easier to learn, maybe frees up some legacy names of older maps, streamlines updates in batches. Less data hoarding, faster backup/cloning, prevent data redudancy on the technical side.
Solution: Pull which maps have been played when. If they haven't been played in over, let's say, 2 years or played once or twice and aren't new, remove them. If they haven't been played it's obvious they're either forgotten, or not one player wants to request to play them.