This decision of the Ministry of Commerce of Indonesia is caused by the fact that they do not want to recognize cryptocurrency as a digital kind of money. It is possible that it is advantageous for them to consider cryptocurrency as a commodity, since in this case they can get additional income by charging value-added tax.
Crypto cannot be a legal currency in Indonesia because the laws only allow Rupiah as our legal currency. So, there is nothing to do with the policy made by our ministry of commerce. Please, check again the laws related to legal currency in Indonesia. Even, dollars cannot be a legal currency in Indonesia.
About the advantage to allow it as a digital commodity, it is true that the government is possible to earn taxes from this decision. But the tax object must make sense, it shouldn't intervene in any crypto exchanges in Indonesia. Trading activity in an exchange cannot be taxed, it is the own business of the exchange. The tax may be possible when the crypto holder wants to withdraw their asset to the banks.