I love trackballs but having lived with a guy who used a trackball mouse to game whilst eating, the thing needed disassembling for cleaning somewhat regularly (Dorito dust…) so I imagine that’s why these things never took off.
Owning and still loving the Steam Controller, the haptic concaved trackpads could be set up to really feel like a trackball and, in my opinion, had all the benefits of the trackball without the downsides.
Man, I wish Valve would release a Steam Controller v2 :(