Most of that number of people have English as their second language. Even then, you have to wonder both how much of that is: a) interested in watching streamers, b) interested in anime, c) even willing to give VTubers the time of day. Historically, the most popular stream times in terms of viewership has been NA primetime.
That is to say, I still think Cover should make a better attempt to break into the market than they have. Just because all of the above is the case, doesn't mean they cannot carve out a dedicated viewership there. I just understand why they haven't tried.