I don't play a lot of Nocturne, but I do know that he used to build like a bruiser or even towards the tanky side, yet even at professional level he seems to be played as an assassin now. Why is that? I legitimately don't know.
Because unless you synergize with a defensive item like Spirit Visage, there's no reason to build a defensive item when you could just one shot the enemy by keeping up with any defenses they gain with offensive items.
Isn't he originally an Assassin champion.
because they buffed his ultimate and now he has a much easier time . . . . . . sorry noc just ulted and I think adc just died we couldn't see. what were we saying
In the past when fights dragged out longer, he would ult into the back line and build bruiser to kinda tank ADCs a bit while he pummels a target.
Nowadays divers just don't really succeed so they either go full tank or go full damage, in noc's case, he's most useful ulting and deleting a target with lethality and duskblade, because as long as he takes somebody important with him, his job is done.
Damage is high enough for him to just kill standard carries. He's currently my favorite jungle if I ever have to because it's impossible to be useless.
Cause :
A. Conquer on light fighters make it impossible to build defensive anymore on 
etc
B. As someone said down below, defensive items doesn't work with champions like him and wukong well anymore.
C. Cause 
working so well together, yet people this days blame kit while it the problem of it allowed to work with cause most divers and assassin abuse them together now.
