Ollie was asleep at three in the morning when the Discord app on his phone started blowing up. He panicked; many of his friends lived in different time zones, but they knew how late it was for him.

These days, “mcyt” starts trending on Twitter at least once a week. It’s an acronym for “Minecraft YouTuber,” but that’s a bit of a misnomer. Yes, there are YouTube videos — many with absolutely ...