Part of the issue, beyond magic being a good solution to a number of problems, is fueling the magitek. Garlemald is located over actual rivers of Ceruleum, which they use to power their mini gundams and airships. Eorzea has significantly fewer deposits and most of that gets exported due to Ceruleum being too volatile for most purposes.
The Machinist notably does not use Ceruleum powered machines, they instead use a device called an Aetherotransformer to convert pulses of their own aether into lightning aspected energy, (this is also why Machinists don't need to reload bullets, so long as your hearts pumping you have infinite ammo). Of course these devices seem to cap out at slightly larger than a Roegadyn as only so much energy can be stockpiled. Machinist is also a fairly new discipline, enough so that the soul crystal recieved for it has nothing inscribed, it's there to act as the power source for the Aetherotransformer.