( mako hmms thoughtfully as the dummy rights itself. )

Mm. Honestly, it might just be a matter of if and where it's being taught. Bending subsets are incredibly rare to begin with — maybe one in a hundred, and in most cases they still have to be taught, rather than something people can accidentally stumble on. People learning on their own without guidance... maybe one in several thousand. As far as I know, only two firebenders have mastered combustion in the last hundred years, but it may honestly just be a matter of it being a closely guarded bloodline secret.