Debating is not on the usual school curriculum in many (most?) countries. You'll usually find private debating clubs, but they're also often not a big or even usual thing. Hence often not even known about.
What I do not understand is how you could be completely ignorant of the idea of "debates". There are thousands of videos on YouTube of debates. How can you understand the definition of the word debate and not realize that people have debates?
To me, that's like saying "I didn't know science fairs were a thing". Sure, I can understand how many (most?) people have probably not participated in a science fair themselves, although I made my initial comment aware that this is Hacker News and it's a slightly different group of people than the population at large. I do not understand the level of myopia that would be required to not even realize they exist.
As to debates, I've come across several debating clubs and public speaking clubs, however when I think of "debate" I think of American elections with politicians on a stage with podiums - we don't really have that here, especially between parties.
Also, I'm not American.
I know what penguins, stoning, and The Great Wall are, even though I live in the US and those things aren’t common here.