What purpose does disease serve to make the game more fun?

I really have been scratching my head about this. Why does mob have disease actually? What purpose does it serve to make the user experience more fun? It was already kind of annoying with the skeletons and mages and whatnot. But these disease beetles.. hello?

Seriously the only purpose these disease beetles serve is to make people annoyed at the game. Please get rid of these beetles. And take a second look at how long disease should last when inflicted by mobs or better yet just get rid of it from the mobs. Make the mages and skeletons shoot fire at you instead. That would be way more “fun”