At Nationals, why is there only 1 timekeeper per lane?

Hello Ben, Actually there are no timekeepers appointed at a National level meet. What you are seeing are IOTs pushing buttons for a backup to the backup system. The main timing system at this level of competitions is the touch pad with the overhead cameras being the secondary or backup system. The buttons are used only if all else fails. Please note that if the button time is used – which is extremely rare – then this time would not be able to be used for record purposes.