It is not a plot hole, it is just something that if the reader notices, it may break their immersion in your story. Your story has to make sense, things have to follow.
You can indeed have things that are unexplained in the story, readers are not going to think too hard.
In your example, we have all kinds of technology in the real world today, but most of the world is still quite poor. Most of the USA is still quite poor, living paycheck to paycheck. We still have homeless people wandering our streets. My local Food Bank feeds literally hundreds of thousands, and would feed more if they had more resources.
This all depends on the power structure and wealth structure in your society. Coal and money and railroads don't change those dynamics, they may be for the upper 10%, not for the masses. In the middle ages, kings and their extended family could be quite rich, living opulently, while many peasants literally never saw any money at all. They were all "work for food and shelter" citizens, farming for Lords, servants of Lords, etc.
Nobody will question why you have coal and railroads, but the majority of people are poor.
The one thing I'd be careful of is a dynamic that is still playing out today: Machines take jobs.
Some people used to dig for a living, but the steam shovel killed most of those jobs. Some people cut and threshed wheat for a living, but a steam machine can replace those jobs too.
If you have trains, you have steam engines, and steam engines can take all kinds of jobs that depend on muscle.
Just like today, robots and AI (machines) are taking manufacturing, shipping, and all sorts of jobs, all the time. Not humanoid robots, but robots:
At one time, Frito Lay's #1 kind of job was cookery, actual people preparing farm ingredients and making chips and snacks with them. No longer. Frito Lay's #1 kind of job is engineering. Virtually nobody is doing any element of the cookery in a modern Frito Lay factory. Robotic machines receive the raw farm goods, dirt, leaves, bugs and all, and do all the cleaning and sorting. Robots peel and slice the chips, shuck corn and strip the kernels from the cob, cook, grind, inspect and reject, bag, box and put products on the trucks. Everything. And if the robots detect anything wrong, they can automatically shut down the line and alert an engineering team to come check it out. The human workers are often just the ones driving the trucks with a farm harvest to the plant, and the products away from it -- And Tesla is working to hard to replace them with robots too; self-driving 18 wheelers.
Early in the history of trains, it was humans hammering in the spikes to nail rails to cross timbers and make the railroad. But the steam hammer soon replaced those beefy fellas. If your society has had railroads for more than 50 years or so, I would need an explanation as to why the steam engine was not ubiquitous for doing all sorts of heavy muscle work. Otherwise, common sense and realism would be broken, along with my reading immersion.