I just uninstalled a few games from GOG and it left a bunch of files inside the folders. I wish it would clean them up.

Get Geeksuninstaller and nothing will be left.

I think this is intended, at least for some games, so you can keep your savegame files. Did you get a message asking if you wanted to keep them? If I remember correctly, it should also tell you that deleting savefiles will completely delete the installation folder.

That’s just windows, the uninstall rarely removes everything from an item. Have a look I programdata, %appdata%, and other areas. Some applications, not games so much, are specifically designed to be hard to remove, leaving things all over. It’s a reasonably small part of housekeeping though. Minimal installs, cleanup once in a while.
It can sometimes be beneficial, such as the save games mentioned above, I once lost a load of in game pictures as I uninstalled which wiped all.

Even worse, the uninstaller found NOTHING when I tried it the other day. Weak, GOG, weak.

The Everything uninstaller worked though.... wait... chhhzzzzz...

Here is an old joke: Cannot find A: Formatting C: instead. When you were formatting your new diskettes.