I LOVE me some trains! I think what you are hearing is that there is a variety of opinions that are being expressed that may agree, or not, with your views. I will gladly talk about trains all day, into the night, and the next day, too.
The point here is that you are expressing a view that is, in some instances, not matching factual data. Since grav technology does not exist we can only extrapolate from today's tech and the past century of so since trains exist. As others have pointed out, the concept of trains is no different than that of wagons or barges - each follows the path laid out for it. Ocean-going ships and trains are more comparable in that sense as they are able to (almost) go anywhere their medium exists.
The challenge you are facing for your supposition is one of cost. A single grav train car is not going to be cheap. A grav rail car is going to be a rough equivalent to a double-sized air/raft. Assuming just lift and some possible aerodynamic controls and other features you are looking to an approximate cost of Cr750,000 to MCr 1. That's a best guess based on what already exists in the books for vehicles, could be less, but it's a fair cost. We don't have any idea of the difference in costs for grav units that are lift only, vs lift-and-drive - or if that is even possible. So without that we just kind of have to leave that to the side. Some argue contragravity is lift only, with a different mechanism for horizontal movement. But this is getting away from the discussion.
So it comes down to the same questions we have today - is it cheaper to have fixed routes where you have fixed costs and cheap (relatively speaking) rolling stock, or not? If you want to have this argument you have to also consider the fixed cost for EVERY grav-equipped car, and just how much money you will have sitting around idle waiting to be used. The more expensive a single car is (especially with low utilization rates and long dwell times), then the higher your costs will be when it's used. An OTR tractor trailer is super-common, and while not cheap, they are relatively inexpensive. Non-specialized rail cars fall into a more expensive but similar idea. Each time the sophistication of the transport type increases then it gets harder to have more vehicles. Airlines have spare aircraft in case one goes out of service in an unplanned fashion, but there are limits to how many they can afford (and smaller airlines cannot afford any). It's very scalar and easily measured.
So I don't see this as it couldn't happen - but I do see that your insistence that it would happen along the ways you mention have a reasonable explanation as much for it COULD vs it WOULD. This is a game and we already know the economic model is shiite. But it's not meant to be an accurate simulation, so shiite works. All anyone can do is speculate and try to apply actual real-world examples to things like this unless you want everything built upon hand-wavium (and that occurs far often as it stands). I prefer a reasonable model built upon reasonable assumptions and extrapolations with a modicum of necessary hand-wavium that fits the game model. We aren't' talking about space orks who if they THINK it will work that way the universes' rules are bent to make it work that way.
I think it's entirely fair for people to disagree, and agree, with anyone posting their opinions in a public forum. If all any of us want to hear is our own voices then we have small enclosed spaces for that. Otherwise, if you are posting here expect people to disagree with you - sometimes politely, sometimes impolitely and rather vociferously impolitely. Welcome to the Interwebz!
