To cut down on the signal path and chance of failure.
Why not use the dumble style of foot switching and only use the relay as the switch with a manual control. Wire it so if the relay fails it defaults to the way you either prefer bypass or loop.
nick
The dumble style of switching relies on the functioning of the relay, the switches (on the rear panel and the footswitch) only ever switch the 12v control voltage, not the signal routing. I wanted a quick and easy method of bypassing the whole rack if I needed to, just like in hardbypass fx pedals.