I don't want this to be a discussion of the reality of steam engines, that they were replaced because diesels were more efficient, etc, but rather about the magic of them that still seems to catch the eyes of people, many of whom have never seen one in real revenue service (I certainly didn't). And no, I don't think bringing back steam engines as some have suggested, is gonna bring back the golden age of railroading or big coal for that matter, the age of the steam engine passed a long time ago.....
The other night, there was a Lexus commercial (why they sell cars as holiday gifts I'll never know) and in the commercial there is a young girl imaging herself in the cab of a steam locomotive as her dad drives by in his new Lexus. Obviously, the advertising people who came up with this thought the image would do something, but why, if few people under the age of Social Security ever saw one?
Likewise, I have seen several ads featuring toy trains (a toyota ad, another one was shot at someone's home), and they show a steam engine puffing along.
Personally, I think it is because the steam engine , because of the way it looks with all the external piping and steam and smoke, looks like some sort of imaginary beast or maybe a dragon, and I think that is why it catches even kids attention, and I suspect it is why even today so many who get into trains have at least some steam on their layouts, even if they otherwise enjoy modern trains for the most part.