Necessary may not be the right word, even if I kind of feel that way.
To me, they made the movies, great movies. Then they did the Hobbit, which was good, but not great. And now out of source material, doing something more feels unnecessary because they have a great and epic story already done. Adding more to it, is going to likely water down the whole product. To go along with Star Wars, they basically killed it by watering down the product already with too many movies and tv shows that have diminishing returns IMO. Marvel has done the same thing. Now they'll milk LotR universe.