Yes, the government is not as naive and stupid as we think, they know everything about bitcoin and they even know more about bitcoin than us and that is why they are harsh on bitcoin. They realize that if bitcoin becomes popular without control and people freely use it, their power will be shaken and even collapse. The government understands bitcoin very well and has always tried to stop it from the very beginning but perhaps they failed, and now bitcoin has become so popular that it cannot be banned. They began looking for ways to legalize it with a series of regulations, and the hope that it would be controlled and would not let it affect their power.
The government can still ban and restrict their citizens from using whatever they feel is a trait to their economy, even if that's not the main reason for the banning. You say they can't ban Bitcoin, and I completely don't agree with that. All they have to do is place a ban order on it, and whoever ever uses it will be punished; that's all.
What the government is banning is banning people from using bitcoin, they are ready to impose heavy penalties if someone stubbornly defies the ban. But even so, can you guarantee that people will strictly comply or will they still quietly invest in bitcoin? For example: Bangladesh is a country that is still harsh on bitcoin but did you know that many Bangladeshi are still investing in bitcoin and some are even active on our forum? Governments can only issue bans on their citizens, they have no way to completely stop bitcoin.
On the side of regulating it, they have already seen that there is no way that they can control Bitcoin, so what they are doing now is regulating those firms that deal in bitcoin through those centralised systems. Now they can control how their citizens make use of Bitcoin, tax it, and freeze user accounts, which makes it very easy for them to tackle and still control.
If they could have banned it they wouldn't have legalized it with a bunch of regulations, they clearly failed to ban it and instead were looking to control it. But how effective the control is depends on each government because as far as I know, many investors still avoid taxes, including you and me. I guess you yourself are using bitcoin to avoid taxes, so how do they control you?