In fact the mitigations have been so effective that in practice stack smash attacks are mostly historical at this point. But yes: having the direction of "natural memory copies" be the same direction as "back into the caller memory on the stack" was clearly a really bad mistake in hindsight.

I actually don't know where it came from. It was true in original PDP-11 Unix for sure: you had the program text followed by a grows-up heap, with the grows-down stack placed at the top of the program segment. Interestingly PDP-11 addressing was general enough to have implemented a grows-up stack, so this is clearly a mistake Unix could have corrected. I just don't know if this was the original use of the convention or if it inherited it from elsewhere.