Regulate what's within your jurisdiction. That's all any government can do in any circumstance. If regulation results in more friendly advertising that's less likely to have users reaching for the blockers, then those advertisers are going to be more successful, and so even those in unregulated countries will need to conform in order to compete.

That's assuming that the number of users that have already reached for the blockers are of a significant enough percentage to make a difference to website ad revenue.

Start somewhere or stay nowhere.