Why do we have abyss spawn in boss room?

I am grinding xp in the mid 90's with omen to prevent xp-loss. It's tedious

Now I killed a boss, and 8(!) abyss elite monsters with both anti-refresh ES aura and "all damage chills" spawned in an instant after I downed the boss.

You don't have a chance with 8 of those wrathful crearures in a small area, no realistic way of escaping. I had to lure each one out of the boss room and kill them separately. Luckily I had a 1 revive map.

This feels just meaningless, why have an option where you just can't survive, no matter how strong your build is. I even prepared, so I had full mana and full ES, I stood by the exit of boss room, but there was no chance to survive. Those monsters doesn't make me sweat in t15 and t16 abyss, my build isn't really underwhelming

This isn't fun gameplay and just a mean thing to do. From here I will just skip the boss room when I know it has abyss in it