Ahahahaha some people man....
So you go into wolves den... In the 1vs1 arena... The literal only place where you can duel outside of pvp content, and you get duel requests and hate that? Like wtf are you doing there then lmao? That's one of the worst arguments I've heard, that place is solely supposed for that: to have duels with randoms..
Same with the triple triad salon guy, you go into the area where people do their triple triad tournament and seriously except nobody gonna play the card game with you? Like why are you even there if not for the card game...?

It's fine if you don't like it, but those reasons man are just bullshit xD

On a more serious note, even if we say it would be implemented, PvP adjusts your HP down to 10-20k HP. Mobs could one shot you, you don't really have a level either, you are not supposed to take critical dmg and what else... So if they make you immune to mobs, it could be abused maybe and lead to griefing .. Not good.
It needs more natural 1vs1 or 4vs4 duel casual arenas in the open world at a few places(a gc place like one for flames/adders/mael, where they train their recruits, gives it some lore too) but not the ability to duel everywhere(because pvp skills and pve just differ to greatly to coexist on the same map)