Many Martial Arts give you ideas how to kick punch and defend. However, they don't give you comprehensive principles.
With the principles you can apply to test the common elements of the whole system and see for yourself if a particular technique fits the system or just a collection of rubbish.
Many times Martial Arts principles are based on tradition and sports, but not self defense.
Well tradition is just one way to explain it, but the word is too vague. Perhaps, tradition means in this sense that students respect their teachers without questioning the do this do that and that’s it.
Same thing could have happened to their instructor. The problem is filling gaps quickly without design. Someone was missing a kick so he looked at another sport or martial art and thought that this is what it should be without understanding how, why and how not and why not.
And if that was not the case in this generation it was the case in the prior generation. Perhaps in one generation or link of the chain it was that someone did not even think about all the how to why how not and why not. Perhaps he just did not get the right conclusion lacking experience or judgment.