So a few days ago I saw a blog by Ender_Knight56 and it inspired me. So you know how Endermen hate Endermites. Well, this must mean that the Endermites are an infestation of some sort and the Endermen guard the End and Ender Dragon from them. I don't quite know about Shulkers but I'm open to suggestions in the comments. Also please check out Ender_Knight56.