Because you have two current carrying conductors. You have two number 2 copper cables. You can't put 200A on one cable, but your home if you look at it should have a cable marked red and a plain black one. The way you're picturing it would be 200A divided by one wire equaling 200A per conductor which I agree is an overload, but it's really 200A divided by 2 wires meaning only 100A ampacity per conductor and even that is not the continuous load because it's considering your garbage disposal which is only on for short bursts, your washer, dryer, refridgerator compressor, etc. all large amp currents that are only on for a percentage of time. Jesus Christ bless you.