Why GGG limit only 3 mercenaries?

Why I can play 10 characters,
and I bought gears for mercenaries already.
Why you limit only 3 mercenaries,
and prevent players from keep playing?
I really dont understand.

I Think the mechanism is half-baked.
I agree that more storage slots for mercenaries should be added, and there should be an interface that allows me to switch and view my mercenaries’ equipment and status.

Memory limitations. In principle they could produce a work-around but in their design schedule there simply isn't time - we got two very barebones patches and they immediately moved onto the next thing.

That obviously sucks i'd like more slots too, but players also want the next thing.