Because being an American citizen is like having insurance as I clearly stated before. Also before he got the benefit of being American even though he was living abroad when he took the Rhodes scholarship.
If he doesn't want to have "being American insurance" then yes maybe he should give up his citizenship.
Had he argued just for less complex rules and regulations then I agree but that is not all he is advocating.
He is telling US taxpayers hey keep the country going, I am not going to contribute anything but I want to be able to easily comeback if I need to.
What's so extraordinary about "avoiding" to pay taxes for services you will not use?