Looking at the mission website,[0] there are still a lot of people involved with the mission, spread across science, engineering, operations and management.
You would be surprised how much science can be done with an old mission like this, both with the data they already have on hand and with new data. It looks like they have several dozen scientists working on the project (not all necessarily full time).
In any case, putting this into perspective, I don't see how it could be a waste to spend $14.7 million / year to keep one of the most distant probes humanity has sent out into space working.
You would be surprised how much science can be done with an old mission like this, both with the data they already have on hand and with new data. It looks like they have several dozen scientists working on the project (not all necessarily full time).
In any case, putting this into perspective, I don't see how it could be a waste to spend $14.7 million / year to keep one of the most distant probes humanity has sent out into space working.
0. https://pluto.jhuapl.edu/Mission/The-Team.php