You're right about that and I don't think it's a minor thing. One reason is that most tutorials have a hard enough time going through everything you need to know before you can start parsing json and writing out to file, without getting stuck in infinite recursion etc. so the nitty-gritty of day-to-day programming work is often left as an exercise for the reader.
On the other hand, I have the feeling that many people check out Prolog to see how it's different then go looking for the way to do the usual things in it. This may be the wrong approach. Prolog has some advanced features and those are "the whole point" about the language. If all you'll ever need to do is process some csv, there's probably no point in going through all the hard work to learn Prolog- you can do it in another language rather more easily.
That said, the Swi-Prolog homepage has a link to a good tutorial on creating web applications with it that I recommend to anyone interested in that sort of thing:
It's under the "Tutorials" header. Unfortunately my phone's ISP is blocking it so I can't link directly to it. Harumph.