Epic Games closed out their latest chapter in Fortnite with an event known as "The Device." Much like their previous event, "The End," this event effectively destroyed the map as massive explosions caused the island to sink beneath the waves. While there were undoubtedly more players this time involved in the event this time compared to last year's, there's also a curious datum: it was not the entirety of the Fortnite player base.
In point of fact, Epic Games indicated that they deliberately capped the number of players who could participate in "The Device," allowing some 12 million players in, but turning away millions of others. Presumably, it was a "first come, first served" sort of basis, as there's been no mention of any sort of ranking criteria which guaranteed access. For those players who couldn't get in, they were relegated to watching the event either on Twitch (who tallied 2.3 million live viewers) or YouTube (peaking at 6.1 million).
Limited events are not entirely new. Some instances of limited events are contingent entirely upon things such as character level or proximity to where the event is occurring. Others, such as the "Blood Plague" event from World of WarCraft, are entirely emergent. And while server queues are not exactly new, nor server stability being impacted by active connections at a given time, it is unusual that event access and server access should be so intimately linked in this instance.
Epic's official response via Twitter indicated they had put the cap in place as a means to ensure server stability. However, the cap seems unusually low compared to the nearly 28 million players who were present during the Travis Scott concert. Reports indicate that because the concert event was spread out over several days, the number of players were present are an aggregate number rather than a concurrent number. Even so, Epic has promised that future events will have greater concurrent capacity built into them.