Why are NPC parties so bad?

[Thangil]

if you do trust party and try to pull more then 1 group at once, well, you bet, healer can't keep up with healing, tank isn't tanky enough to deal with them, and DPS doesn't use aoe, that why trust party only for people that enjoy lore or just want to afk through most dungeon, if you search a fast way to level up better do it with real player

I don't pull multiple groups with NPCs.