The general idea is that mobs are stupid. Their articifial intelligence is not good enough to counter all the different things players have to offer.

Mob can't run when the three of you attack him, nor can he gear for save vs. paralysis to counter you neuro disruption, etc.

Overall, if one could neutralize mobs like this, it would have been too easy. Making things balanced again would require a lot of mob artificial intelligence improvements, and generally it's not considered needed, since most important fights are PK ones.

'Contrarywise,' continued Tweedledee, 'if it was so, it might be; and if it were so, it would be: but as it isn't, it ain't. That's logic.'