That's true but not relevant to the spirit of the point.
If someone mails $ProhibitedItem at a USPS to the UK, then it's the job of local UK police and/or customs to reject the parcel if it is prohibited. It's the UK's problem, de facto if not de jure, because the sender is out of reach.
If someone with a UK subsidiary and local processing center mails $ProhibitedItem to their center and delivers it to someone in the UK, then that's more than the UK's problem.
If the government thinks there are ones and zeros on the internet it’s citizens should not be allowed to see, they should block them from entering the country.