When a server sends some state to a player, they player can’t get a response back without a round trip. The same is true in reverse. Further, the path through fiber optical cables is not the strait nor are fiber optic cables a vacuum. Using lasers through a vacuum tube strait from the user to a server on the other side of the planet might hit 134ms of light lag which is already a significant issue for many games.

PS: LEO satellite constellations like Starlink have a lower theoretical latency around the world than fiber as the signals are traveling in space, but a longer path. Significantly beating that is going to require magic aka a useful fundamental change in the laws of physics as we know them.