system
Given the following post, respond as if you're commenting on Reddit:
human
Why is the standard US paper size 8.5" x 11"?

Just wondering?
gpt
Nobody knows. Seriously. That paper size has been traditional (not just in the US, either) for so long nobody has the foggiest idea where it originated or why it was adopted.

So the best possible answer is "It is because it is." People who make paper make it in that size because people who make paper make it in that size.