I have never understood what need there is for any translation of anything into Latin, from a reader's point of view. I can understand why someone might want to translate something modern into Latin, as an exercise, but I can't fathom who would be the audience, given that there can't be many people ignorant of the language of the modern text but fluent in Latin, who would seem to me to be only ones who could logically be interested. Obviously I'm wrong.
Some translated works touch upon the realm of Romans or Latin. The Asterix comics, for example, play in the time of Caesar ... It could be possible that somebody who likes to read them (and who knows a bit of Latin) would be curious to see what they look like in Latin. And comics are easy to digest ...
It could be a similar thing with Harry Potter ... I can't really judge that because I've never read any of the books in English, but there seem to be a few spells in weird Latin and maybe it touches upon a few myths, so as to entice some interest in what it would look like in Latin? I don't know.
I suppose in most cases, the motivation for readers is similar to that of translators: These want to practice Latin composition with some of their favourite, those want to practice reading Latin with some of their favourite works ...
There are also people who try to read such stories in school on the grounds that they may elicit more motivation and that the stories are often already known (which especially facilitates the pre-reading phases). I'm not a great fan of that ... not only because a lot of translations are bad, but also because it defeats most of the purposes of learning Latin ... but maybe you can throw in a well-translated short story or an excerpt in the transition phase from the textbook to real literature.
What I would find interesting would be some free composition of new stories in Latin ... but no one seems to have tried his or her hands on that so far.