Fiber optics busses were considered for the 777, and were used for the non-critical Avionics LAN. Fiber optics were rejected for the critical systems busses for several reasons.
There was not enough in-flight test data for fiber optics.
Fiber optics require special connectors, and a greater deal of skill to splice when they break than wires do. This was cause for concern in terms of maintainability in the field, and overall reliability.