[GroundUrMast]

FWIW the current carrying capacity of #6 AWG is about double that of #10 AWG. The voltage rating is for the insulation... Grounding and bonding conductors are not required to be insulated so you can use conductors with an insulation rating of any value.

My speculative answer is that the requirement is based in part on the extreme currents that will occur in the event of a lighting strike or heavy power fault to any part of the buildings electrical system which would force current through all all the available paths to ground...

Consider a situation where the power company's transformer suffers insulation breakdown or storm damage causes high voltage to come in contact with the service wires from the pole to the building -- In this case one would want all that energy to have a low resistance path to earth (ideally the electrical service grounding electrode system is supposed to provide that low resistance path). If your antenna system has a connection to earth by way of a rod of it's own, it will share part of the fault current. So the bonding jumper needs to be big enough to carry the current during such a fault. If you do not add a ground rod for the antenna system, a heavy fault current to the electrical service wouldn't have an intentional path to earth through the mast or coax bonding conductors, so they can be lighter gauge conductors than when an added ground rod is involved.

This argues against adding ground rods when installing an antenna system. By adding a ground rod separate of an existing electrical service grounding electrode system, you introduce what is called a ground loop. You then have to consider what will happen if there's a fault to the antenna system or the rest of the electrical system. Where the fault occurs will determine which direction current will travel in the bonding conductor between the antenna system and the rest of the electrical system. When a ground loop exists, fault currents that are less than the trip rating of a fuse or circuit breaker will persist and as a result, there will be voltage drop from one end of a bonding conductor to the other per ohms law. The voltage would likely be far below a danger threshold but may be enough to cause problems for electronic equipment. If you opt to add a ground rod, the heavier gauge bond will have less voltage drop if current does occur, that and the heavier gauge conductor will not fail at the lower current that would cause a light gauge conductor to fuse open.