Good news, it isn't US only (anymore)! Criterion used to be available through Hulu (US only), then it was available through another streaming service whose name escapes me, but they (Criterion) finally started running their own VOD Netflix-like service:

https://www.criterionchannel.com/

I have it setup on my Apple TV in Canada and it works great. Highly recommended!

EDIT: Just checked [0], it's actually USA + Canada only for now... Sorry about that.

[0] https://www.criterion.com/faq/channel