If the company or a person running a Defi protocol is able to hide their identity, there's no way for a government to regulate them directly. However a government can always use a strong internet firewall to restrict access for it's citizens. So indirectly a government can regulate them.
Defi is posing a huge risk in the mainstream financial market today as it is very very easy to convert the black money into white. So it's a security risk as well as these can be easily used to finance terrorism activities and any kind of illegal money transactions.
And if we want to keep current form of civilization that has taxes, we need to have transparency on wealth and AML laws. This is where FATF comes in and basically renders any cryptocurrency unusable that you can't prove where you got it from.
Things have become way more complex and while it's still possible to launder money i am not going to give any examples how to do that as i don't think it's ethical. But DeFi is not the key element in that.