Why is it OK to have multiple bosses spawned but not normal force spawn NMs?

[Tsukino_Kaji]

Why is it OK to have multiple bosses spawned but not normal force spawn NMs?

I'd caulk it up to laziness and the same reason why they didn't add multilples for KI NMs. Whatever that it.

[Kristal]

I'd caulk it up to laziness and the same reason why they didn't add multilples for KI NMs. Whatever that it.

The criteria for multiple ??? seems to be:
* drops items for empyrean weapons
* zone bosses and their overlords

Adding multiple ???s for every KI NM would likely be too much for a zone. SE would have to reduce the number of mobs.