YouTube does this too. We immediately fetch the remote and mute the damn thing. And I'm contemplating finding something that auto mutes for me.

For us, even regular YouTube is substantially louder than any streamer. If we want to watch something on YT than go back to Hulu/Netflix, we always have to adjust the volume. I don’t get it, why, why?

Louder content is more compelling (to a point), so I'd imagine that louder content helps boost watchtime, which is what both Youtube and the video creators are optimizing for. The music industry's "loudness war" seems related.

https://en.wikipedia.org/wiki/Loudness_war

that's odd to me because a lot of the time I've found that regular YouTube content is on the quieter side to other services.