This is quite a slippery slope. If I host a website in one country, I do not necessarily care where people access my website from. It is not like I actively provide a service to them - they just use internet (decentralised network) to access it. What if I publish a newspaper here, someone takes it where the contents are illegal, am I accountable?
USA (Kim dotcom)
Russia (Skripals)
China (Teng Bio)
Israel (Mordechai Vanunu)
It makes sense for treason to apply everywhere. If that were not the case Britain could not have executed Lord Haw-Haw given that he only sent broadcasts from Nazi Germany.