The tubular structure of most large rockets is well suited to withstand many gs of load along its axis. It's also quite fragile wrt side forces and bending. Making it stronger makes it also heavier.

A device that can carry several tons to GEO and to start in a slanted position along a mountain would be a very different beast than a usual rocket.

To say nothing about building several miles of an excessively straight maglev bridge along a mountain which is likely not that straight, and also highly visible.