I think that it is because most still photographers don't need the robustness of Matthews (www.msegrip.com - Matthews Studio Equipment) gear, and that robustness comes at a price so the cheaper, lighter Manfrotto/Avenger gear is just fine. They also tend not to use the same wide range of lighting setups <duck> so they don't need the 'whatever you want we can do it with what we have in the grip truck' sort of approach.

In the hills in winter I would prefer not to cart anything heavier than it has to be, though I admit that the experimental spoon with lightening holes was not a total success.

Best,
Helen