It’s simple, there are really 2 people right now – those that want followers at end-game and those that don’t want followers at end game.
If you make followers viable for end-game then you pretty much have to make the end-game viable to account for not having them also.
So, now you have people asking the designers to pretty much balance an extra-end game element, on top of the already planned solo(Without followers), duo, trio, and four player modes.
I, for one, don’t just assume that’s something that’s easy to do.