I kinda agree with the tweeker remark.
It is the easiest way to make a motorized anything, and now, the majority of people you see riding them (in my area) have some f'd up piece of crap bike, no helmet, disobeying all known traffic laws, and usually look like the tweeker homeless type.
Back in it's heyday, 2011-ish, there were a lot of really good builders out there, building bikes that would put most moped builders to shame.
Modifying or handbuilding frames, custom made gas tanks, pipes, etc.
We had rides in LA and OC with 50-100 riders, and it was almost a competition to see who could make the coolest, fastest bike. The creativity was amazing, and it was much more than slapping an engine on a junk huffy, or putting mags on your stock moped.
There was a lot of innovation going around, as performance parts weren't available yet, and many people I know used the China engine as a stepping stone, going from no knowledge of anything mechanical, to becoming master builders of custom bikes.
There's still a few guys out there doing some pretty amazing things with these cheap engines, and it evolved into better engines, better bikes, using different engines, and for some, bringing the spirit of handmade motorcycles back from the 1900's.