I don’t think that ArenaNet can do much about it since according to their own rules someone “playing” a Necromamcer with Minions or an Engineer with Turrets while watching Netflix and pressing a key once in a while is not doing something forbidden.

And how would you determine whether this someone, their trained cat or a macro is randomly producing those key strokes?

While I personally think that massive amounts of AFK farmesr are kinda immersion breaking, there are far worse shenanigan going on, like botting in PvP.