Why are fantasy settings by and large medieval (and not evolving) probably has some interest (often the setting involves lost technology, "a great civilisation has disappeared". Tolkien does this too, with the silmarils, the fall of numenor). In fact per Tolkien law all the amazing elves are basically dying out and we're gonna be stuck with boring mortal men in the fourth age. So arguably all the good stuff has happened and we're on the road to ruin. Wonder if he read the daily mail?
A significant portion of authors might just be emulating Tolkien, I suppose. Also hard to have a secret elven forest base with high resolution satellite imagery, thermal imaging and precision guided weapons.
You don't need the books though, you can check online to see about the scouring of the shire and Saruman in general, which for the Tolkien case makes his views pretty clear.
If you really want to waste some time, consider that the eagles came and rescued Frodo/Bilbo from mount doom near the end. They could easily have flown them _into_ mordor in the first place, especially since at that time the Nazgul were not airborne, saving a very extensive tour of New Zealand (uh I mean middle earth) in the process. Would've needed far less elven bread and a smaller fellowship and got them more air miles. Gandalf could've also taken a spa holiday instead of an arduous hike, bungee jump with a balrog, death and resurrection, which I'm fairly sure weren't covered by his travel insurance and likely not recommended by his doctor.
Ultimately it is a story. In some senses alternative worlds allow you to compare "what ifs?" and this can be fun. However you have to be careful how much you read tvtropes...