The issue is tied to Elden Ring's current player cap. Multiplayer interactions are limited to four players per world and only one invader, at that. In other words, it's rare to come across a PvP interaction with multiple people. And even if one does spawn into a world with multiple people, it's rarer yet for it to be someone interested in a structured duel or a "fight club." In order to do those bigger PvP events, players need FromSoftware to increase the number of players per world.
A hugely successful post on Reddit shows just how popular this idea is among the Elden Ring community. The post asks FromSoftware to remove the multiplayer player caps to make Elden Ring more like Dark Souls 3. Dark Souls 3, in comparison, had a player cap of six with mechanics to swap the maximum number of invaders and cooperators. This change would allow Elden Ring players to host fight clubs where players could take turns battling each other.
As for whether such a change could be made, it isn't clear. FromSoftware had a similar cap in Bloodborne, allowing up to 3 cooperators and a single invader (though Chalice dungeons allowed 2 invaders). It may simply be a matter of FromSoftware's current online infrastructure being built around 4 players, meaning a change is unlikely to come.
That doesn't mean Elden Ring players should give up hope, however. Many Elden Ring players have called attention to several coliseums within the Lands Between. These coliseums are currently inaccessible, though datamines have shown that they're otherwise ready for use. Player peculation, or perhaps simple hope, is that the coliseums will be a part of a piece of upcoming Elden Ring DLC. These coliseums could be unlike the rest of the game and would allow for bigger PvP experiences.
All Elden Ring players can do for the time being is wait and see what FromSoftware will do next. FromSoftware isn't traditionally a very communicative developer. Post-launch content and DLC are rare. Elden Ring's success could mean things are different, meaning more updates and content additions than usual can be expected. But it's more likely that little will change and Elden Ring players should enjoy the game as it is, holding out some hope for more down the line.
Elden Ring is available now on PC, PS4, PS5, Xbox One, and Xbox Series X/S.