@Dave M,
No, it is not difficult to engineer a motor block. The difficult part is a) determining what the specifications you want the block to stand up to, and b) manufacturing it at a price point that the hobby will buy in to.
As Dave G pointed out his line has steep 4% grades up and down. How much weight do you want that gearbox to withstand? Dave mentioned 10 cars, at say 3 lbs per car, that’s 30 pounds. That can be engineered for. So the next fella says well it works at 30, maybe I can do 45 lbs. I think you can see the outcome. Maybe there should be ratings on the package that clarifies the design criteria? Do some of the manufacturers even know them?
The price point is another consideration. How many units do you think you can sell? If you guess too high on quantity of units, you are stuck with a bunch of inventory that may or may not have paid for itself, and will take a long time to move. If you guess too low, the price point gets higher than the average hobbyist is going to spend and again you have an inventory issue.
As for subways running ‘flat’, I have to ask Where? I have ridden many a New York City subway and they go up and down all day long. 4%…probably not. There have been two article in NG&SLG on underground railways where the owner simply modeled 3 sides of the tunnel and the fourth side was the viewing area. Usually smaller scales though, and I don’t remember specifically if they were a subway.
The issue that seems to bother me the most about model manufacturers (and this applies to not just trains) is that the small amount it costs for a quality product that the customer will be glad to brag about to his fellow hobbyists, (free advertising) well outweigh the negative publicity of poor product construction (or why I personally only own Aristo rolling stock). In our hobby there are no manufacturers with out their issues, some are far better than others.
A disclaimer for Greg. I am not bashing Aristo, just making a note that a number of fellow club members have Arist Mikes with driver issues. I decided I did not wish to deal with that every time I wanted to run a train. My personal choice spoken only.