Not sure whether this still holds for 1Gb and faster ethernet, but there used to be a maximum length due to collision detection. An ethernet frame has a minima

Not sure whether this still holds for 1Gb and faster ethernet, but there used to be a maximum length due to collision detection. An ethernet frame has a minimal length, and since the cable (used to be) a shared medium, frames could collide. Such a collision could be detected by senders whilst sending the frame, allowing for a re-send. However, when the cable is long enough, you could get collisions happen after you are finished sending. I'm guessing that the newer standards that only allow point to point connections invalidate those requirements though.