governments are not almighty.
they havent forbidden cash (ok some are trying to limit it)
they havent forbidden gold
as soon as an economy is using it, they want to tax it - and not forbid it
Try even traveling with more than EUR 1000 cash in France, for example through an airport: your money will be seized unless you can prove why need to carry such a 'crazy amount' on you. The police frequently seizes similar small sums of money during simple traffic checks. They seems to be pretty good at trying to limit it
And as for forbidding gold, governments never did that, right?
https://en.wikipedia.org/wiki/Executive_Order_6102