United States, Mexico, Australia, New Zealand, South Korea.
(If anyone actually wants to know.)
(If anyone actually wants to know.)
Googling around a bit, it seems that Google's attempt to include everything under the sun into your YouTube Red subscription is to blame...
They could just give you ad-free youtube. But instead, they want YTR to include their YTR-only premium content, and also they want to throw in Google Music... all of that requires decyphering copyright laws and potentially registering as a royalties collector (IANAL). Typical Google behavior, an inflexible all-or-nothing approach.