Fortnite’s success has humbled Activision Blizzard, Electronic Arts and Take-Two Interactive, the “big three” game developers

It starts with 100 pickaxe-wielding cartoon characters trying to scavenge weapons before they are hunted down and killed by their foes. It ends with the last player standing. This is the premise of Fortnite, the “battle royale” shoot-’em-up developed by Epic Games, which has upended the video-gaming industry.

Its success continues to humble Activision Blizzard, Electronic Arts and Take-Two Interactive, the “big three” game developers. Shares in the three tanked last Wednesday when two of them published disappointing fourth-quarter reports. Fortnite was the cause, even if they didn’t want to admit it.

The main problem for the big three is that Fortnite is free to play and more than 200 million people play it, up from 125 million last June. Such is its impact that…