It is impossible to approve something that you can not control or where you will not be able to dictate rules. Government can approve things that can become controlled by it fully or partially. What about decentralized things, in this direction government has only possibility to control things and processes that may be connected with crypto for example, your declaring assets in your native money equivalent, or you buy equipment for mining, or licenses for exchanges, but the decentralized thing itself is outside their control and opportunity to approve it.