It's simply to do with trains and forces surely?
Intamin = 2 car wide trains.
B&M = 4 car wide trains.
The reason B&M came up with the wider track was to easily support the wider trains. Intamin can support wider cars now (Furious Baco) with their track design, but it took them a while to get it just right and I think Baco has "beefy" Intamin track.
B&M don't have track like Intamin simply because they don't do narrow trains. It's odd that newer Intamin track is going back towards single spine like B&M now and away from the triangular supported bi/tri/quad track they're used for a few years. That will come down to new production techniques, new design techniques, cheaper manufacturing processes, changes in material/labour costs, etc, etc, etc.
All coaster companies will have two things on their mind when creating track:
- function
- cost
If the cost is too high, then they'll look at a different way of making it function. Cost is not just metal raw materials, but fabrication, weight (shipping), on site costs (foundations, engineering expertise, labour costs, equipment requirements and probably a load of other stuff) and again, a thousand other things I simply don't know about.
In the Dollywood topic, it's pointed out flyers and inverts have "curved" cross ties, the other coasters flat. Why the difference? It'll be cost or function (I'm betting function) and certainly not so you can tell if it's going to be a flyer or sit-down while the track is sitting on the grass outside a park.