ranged attack on every monster?

[Physic]

Which is a perfectly good reason.
And honestly, if they can't come up with an better idea to prevent an abuse of the kiting mechanics than mobs that conjure an infinite number of projectiles out of thin air, they are finished anyway.

this is the usual method, or mobs teleporting, its the fairly common answer in most situations, another answer might be monsters hanging out with ranged monsters in parties.