We have two different kinds of underground caverns, the natural caves and the artificial mines and subterranea. So if a mine is artificial, made by man, what is then the copy of a mine? Artificial²? Nevertheless, there are very good reasons to fake a mine, as there are good reasons for copies of natural caves. And the best explanation is probably a coal mine.
Coal mines are the most dangerous mines on Earth. Coal seams are rather thin, lets say 1 m or 2 m high, and cover square kilometers. Mining a huge layer of rock completely will cause a collapse, leaving pillors will make mining inefficient. Also, especially younger coal seams, have rather soft rocks above and below which will collapse. The result is that many mines are mining the coal and at the same time a few metres away the ceiling is collapsing in a controlled manner. And finally there is the problem that coal is a collection of complex carbohydrates and this includes gases like methane, which when mixed with normal air can cause explosions. So what is the result: there are no abandoned coal mines! If they do not collapse they are filled in or collapsed artificially. If this were not done, there would be a danger of explosion. Not a good prerequisite for a museum that is visited by many visitors.
Now you are the director of a mining museum and want to show how coal mining works underground. Then of course you build a show mine! But wait, there is no disused coal mine, so you have to fake one.
In most cases this is the reasoning for creating a fake mine, the non-existence of a real mine tunnel. And actually it does not matter very much. If the fake mine is in the cellar, the temperature and humidity is realistic, the fake mine feels and smells like the original.
And such a fake has numerous advantages. You can build it where the museum is located, even if there never was mining. You can build it big enough so all the exhibits you have fit in. And it's much easier to keep it safe, install trails and electricity, and even an emergency exit is no problem at all.