UPDATE 16/6/20: Fortnite developer Epic Games has issued a statement on the capacity problems which marred last night’s live event.
The developer said it capped the game at 12m concurrent players with more than half an hour to go before the event was due to kick off. (The game’s all-time concurrent record is 12.3m, for its first Travis Scott concert.) Presumably many millions more would have flocked into the game, or tried to, had Epic not done this.
That said, Epic explained that it was “improving systems” so that more people can watch live events in-game in the future.