The same technology that makes realtime collaboration (e.g., figma) go is the technology that makes it possible to build high performance single-user apps that you can open on your phone and desktop at the same time (e.g., roam). It's collaboration whether it's two users or two devices from the same user.

The web will go multiplayer because it's the only way to make high performance UIs that are multi-device without locking. The multi-user realtime collaboration bit just comes along for the ride.