There have been a couple that have been let go over the years, but most mods are removed just due to inactivity. Quite a few mods seem to get burned out and just disappear. I can't blame them. Hopefully they're sat on a beach somewhere or just enjoying their life offline.
Enjoying their life?
Just curios, did theymos pay all the mods for their work or were they doing it as a voluntary job without any demand of money? If they were not getting paid, I think this could also be the reason why some of them left and got fired from their position.