Why is Hell (גהינום) named after גיא בן הינום , the Valley of the son of Hinom? And what is גיא בן הינום anyways? Why don’t we just call it Sheol like the Tora does?
The Torah (well, Nach, really) does call it She’ol, but it also calls it a number of other names. You can ask on Nach itself: why does it use multiple names and not stay consistent? It’s because, as described in Eruvin 19a, each name has some significance regarding Gehennom’s function.