I think it is because your lever to control the plane does not go up or down but forward and back. and then you pitch the lever the same way you want to pitch the plane. forward to pitch forward and back to pitch back.

Same reason throttles are pushed forward to go faster and backwards to go slower. Except on bulldozers, which have a deaccelerator for some reason. and game controller shoulder levers for ergonomic reasons.

I think if the lever were mounted up and down they(the wright brothers) probably would have wired it to pitch the plane up and down. I am not sure why it was not mounted up and down, probably a combination of arm strength, ergonomics of movement and simplicity of mechanical design.