How do you know there aren't more Chen Xiao Wangs? What makes you think others aren't putting in serious work?
Well, you used the phrase "learning tool", which is fine as far as your description goes, I just question how much they really contribute to learning.
The number of real masters of this stuff is very small, relative to the available pool of practitioners, which wouldn't be the case if all the people who have been exposed to ki tests made good progress. The existence of various tests doesn't seem to be much of a factor in getting people to an impressive level of skill. Some of these guys, like Chen Xiao Wang in particular, are frighteningly powerful. You don't get that just from being told "keep weight underside", and then a few years of pirouettes and you're there. There are bigs chunks of fundamental information missing from the basic stage to the impressive power and ability stage. That all-important information is very closely guarded.