In recent years it's very possible they either don't use a language where that syntax is ever required (python) or just use one of the foreach variants in pretty much every language.
I can only think of Python, but are people learning that alone these days? In every other popular language, I can't imagine not ever encountering a situation where you also need to know the index of the iteration.
They could just write loops and remember that repeating the variable name with ++ is part of loop syntax without knowing what it means. Almost like text-generating AI would do it (ducks).
It also matter that they apparently wrote a for loop a number of times without wondering what each of those symbols actually does and just treated it as magic incantation.
Edit: assuming they didn't use a language where such idiom doesn't exist or is not common, as another commented pointed out.