A lot of it is supply and demand, if a lot of people wanted one, they would be hounding the vendors and someone out there would start making something similar but not everyone out there is doing huge areas of concrete to justify the purchase or need for one of those units.
I agree, it would be nice if vendors were making larger surface cleaners that were motor driven so they could be driven by 5gpm or 8gpm pressure washers.
There might be patents on the swabby and turbo twister which would end up making them a patent infringement to make something very similar or exact but there is enough creativity out there that some new technogy could make something similar, cost effective and affordable.
I like the swabby with the belt driven spray bars so more pressure is hitting the surface, like the turbo twister.
The Turbo Twister is a 36" cleaning deck driven by the engine on top of the machine where the swabby has 4 spray bars driven by a belt which is powered by the zero turn mower itself and can clean a 48" wide path fast.
Both of these machines need a lot of room on the trailer or truck by themselves so it is not feasible for every contractor out there and you don't want one of these for just cleaning driveways, kind of over-kill for driveways but for long sidewalks, shopping centers, parking lots, parking garages, etc.....this is what makes life much better and helps you get the job done a lot faster so you can move onto the next project.