I think the simple answer is that DnD is a game focused on combat, so it’ll have a lot of cool hostile creatures, while Lord of the Rings is focused on exploration and drama, so it’ll have a lot of cool places and friendly creatures.
But when I compile a mental list of all the fights in LotR + The Hobbit, they do feature quite a varied assortment of monsters. Trolls, orcs, spiders, a dragon, a balrog, wargs, nazghuls, ringwraits, wights, the watcher, olifants. Then there are the non-hostile monsters like ents, eagles, ghosts, and shape-shifters.
So I’m not sure the enemy variety in DnD is that much greater in relation to the amount of time spent fighting.
Pretty much all Germans with any experience post WW2 were in some way nazis. As I understand it, you had to be a party member to hold any important job.
Something like an actual true NATO-nazi conspiracy is how nazi chief of staff and war criminal Franz Halder ended up avoiding the Nuremberg trials and working with the US Army Historical Division and the coming founder of the CIA to create the myth of a clean and non-political Wehrmacht.
But any reasonable person will understand that that was an enemy-of-my-enemy kind of deal. (We all know NATO are secretly Islamists as proven by Operation Cyclone.)