Once you've got a steady farm, a nice cozy house, and all the coal and iron, and whatnot you could hope for… What are you supposed to do?
I have a whole single chest of food, a whole other chest of iron blocks and coal blocks, and I'm breeding animals in my expansive back yard beside my 50x70 block garden, all which is beside my massive 3-story house with a bedroom, a room made entirely of furnaces and one crafting table, and 2 rooms of chests. I even have the portals set up, and have no need for my enchantment table by this point.
I'm completely settled for the next 6 in-game years. What do I do now?
And sure, on single-player you might say to go kill the EnderDragon, but what about on a survival server?