A: A footnote is a tiny, often ignored note at the bottom of a page. It's like a whisper in the wind, but with more punctuation.
A: Because our ancestors were bored and liked making tiny, unnecessary notes. Now we're stuck with them.
Or, as some say: "Because someone in the past was a fan of tangential information and wanted to include it, even if it didn't really belong."
A: Ha! You'd be surprised how much you can do with footnotes. You can use them for evil, too.
Or, as our lawyers say: "Don't quote us on that."