Who says? Who is the judge of your work and efforts? My philosophy has always been that if someone is not satisfied with my work then they are more than welcome to put in the effort (months, years) to do a better job. I will look forward to critiquing their efforts .I'm going to say it. What's good enough for me is not good enough for others.
No-one could ever answer that question. I have always built assets that I needed and that I was interested in. I never conducted an opinion poll on what others wanted me to build. Why couldn't they build it themselves (and do a far better job in the process)? Of course if someone is willing to pay me for my time and efforts then that could be a different matter - but I am not cheap. I have expensive tastes in wine and food, a partner and a cat (both with equally expensive tastes) to look after.Also, how would I know what people really want?
My current real-life project, which has been on and off for several years now, is 280 miles in total (including all branch lines) and runs at an average speed of 30-40 mph (in different parts) and would take 7-9 hours to traverse which is close to the actual timetables of that era.Some want an 800 mile route with a 200mph speed limit so you can traverse the line in 4 hours of continuous game play.
Part of the beauty of Trainz is that you can use an existing route in many different ways, most of them were not even remotely considered as possible by the original creator. So some-one runs a French TGV passenger express on your stone quarry route. Let them! It is a hobby and for their enjoyment after all.
Not everyone will be interested in my current project - the historically (or, if you prefer, hysterically) correct recreation of a narrow gauge railway from the 1950s in the Aussie Outback. But no-one is forcing them to download and use it. Just as I am not really interested in North American or European railways of any era. That is another great thing about Trainz - you can pick and choose what you want from the DLS and DLC.
Don't waste time worrying about what others want, do you own thing.
My opinions.