MAKE SIMPLEX GREAT AGAIN!

The longer you stay in a certain area the difficulty for that area is raised and more mobs spawn.

minecraft.gamepedia.com/Difficulty#Regional_difficulty

I'd love harder mobs. But then we'd have to deal with chat firing off how hard it is and everyone dying. Lol.

I usually play on hard myself on single player. That having been said, as meehan said, it only increases damage not number of mobs. I have been playing on the same claim since I started. I had three creepers on my house earlier. I dont need any more mobs lol. I also agree that having it on normal keeps the atmosphere more laid back... I like it as is for multiplayer. Thats my two cents.