Yeah, I was wondering, why has the Y axis always been inverted?

It's because the origin is the top left corner for most things (not just CC) for frames and such, so a greater X value extends to the right, and a greater Y value extends downwards. That way, when you re-size windows, you don't have to worry about the origin moving around, since if you want things to move up with a higher Y-value, that would require an origin at the bottom of the screen.