Bitcoin is not being taxed because it is not yet government regulated. The government has known about it but they can't impose tax on it because originally it is decentralized and it is hard to trace the person in transaction with it. And maybe the reason why bitcoin is not really popular is that the government doesn't promote it to all people because they don't have the authority to regulate it. For me , the only thing that could shield bitcoin from tax issues are the goods and services being taxed.