I think it's because they make it just that little bit differently, and use outdated technology.
Vax etc have only just moved on from single cyclone tech, and their single cyclone was the shit version with the pleated filter in the middle. Now they are on multi cyclonic tech, but tech that is different from Dyson (less cones, shitter design etc) which doesn't work very well as any modern vax clogs it's filter up within seconds. Your picture is such a design, there will be a filter inside the cone, so the way it works will be very different.
It's like the pattern dyson parts, which can look identical, but would be mm different in dimensions, or a slightly different moulding. My pattern Sebo tool set is identical as far as I can tell, but must be different to not have the arse sued off them.
Hoover copied the DC01 cyclone design a bit too closely, hence bye bye Vortex (although when I took one apart they look so different it's untrue), so there is more to it than just the design, it's the process too, mvacs probably knows more on the subject as they have had pattern tools and clips made.