The thing everyone needs to ask before advocating for something "government enforced" is "what would happen if this was in the hands of a hostile government?"
And then remember that (a) just because it's not hostile to you today, doesn't mean it won't be tomorrow, and (b) one man's "hostile" is another man's "utopia."
And then remember that just because Google is not hostile to you today, doesn't mean it won't be tomorrow.
So how do you think a meta noai tag would be used by a hostile government?
It would be something the website owner set.
Step 2: Abruptly switch to iron-fist enforcement where suddenly people get jail time for violations, but only for entities that have been critical of the government.
This is by no means the only or most likely way, just what I could come up with in 30 seconds. There may be much better "evil government" strategies.