Because you wouldn't want a VAT scam layered on top of the carbon trading scam, which is layered on top of the global warming scam

UPDATE 2-France makes CO2 credits VAT-exempt to avoid scam | Deals | Regulatory News | Reuters

LONDON/PARIS, June 8 (Reuters) - The French Budget Ministry has made carbon permits exempt from value-added tax (VAT) in order to prevent a potential tax scam linked to a French emissions exchange, a government source said late on Monday.