Not being a train driver myself, I imagine that it's not as simple as learning the difference between a red light and a green light. Trains are big and complex machines and presumably a driver needs to know a thing or two about how they work and what can go wrong. Then you have the tracks and infrastructure - all the power systems, signals, junctions etc. There's probably extensive training in human factors and safety as well. While many of the concepts behind the aforementioned are familiar to pilots at least to some extent, do bear in mind that courses are designed for those who don't have any extensive technical background. And then it's the practical part, which is likely dependent on instructor availability, just as airline line training. And you would probably need one to know what they are doing and be confident when releasing them to drive a train across the country all by themselves and with a couple of hundreds of people in the back.