There can be quests and other events that don't necessarily give super rare loot... you have to think about the implication of bosses; new super rare stuff from bosses, and to spawn bosses, should have to be added, and stuff for it, etc... then you end up into modded survival. And Minions are a little too convenient.They've already achieved their goal of a Vanilla Skyblock experience, however, once you get past a certain stage, you ask youself the question "What do I do now?". Whereas all of these features will give you something to do and something to grind for e.g. Bosses, events etc.
Minions will also help you grind and just be there for the sake of convenience.
Custom Enchants keep players curious about which enchant does what, which makes it a unique experience.