I'm not an expert on applications of black stuff, but having ultra black coatings can help get away with complex optical designs where you would have flares or

I'm not an expert on applications of black stuff, but having ultra black coatings can help get away with complex optical designs where you would have flares or loose resolution to scattered light inside your tube assembly. Also an optical design that's difficult to pull off mechanically may be easier to manufacture if you just use this coatings inside the tube and on the baffling.