I often play as sup and when ever I need Armor and/ Or Magic resist with AP I have options as.
Armor + AP 
MR + AP 
I know there are AD + health but that's not the same. There are no AD + Armor items or did I not see them.
Any good reasons not to have them ? If 
can exist ( without it's lifegrip passive) so can AD+Armor item.
those items all have something else added to them that makes them different for example passive is the main reason you would buy that over say 
to help with extreme mana problem champions. abyssel helps due to the fact of the aura shred. it be kind of hard to introduce this into the armor and damage items i mean like... pretend its ad. so add this a 
and throw it on 
. this would properly tip wukong over the edge.
or for example .
your nasus and you rush this vs any ad top laner and your literally never leave lane... or yorick considering how cheap the item is having basically permanent mana due to passive that early in the game would make some extremely toxic top lanes with endless ranged poke. (one of the reasons yorick is in a week stat. not for balance problems but because hes so toxic to lane against) however i am sure that once they find a passive that would fit with this type of item they will test it and release it. Riot doesnt really like releaseing (just stat) items i mean your pretty hard pressed to find an item above 2000 gold without some active or passive which be one of the core reasons you buy it.
There are armour items 
that provide a passive with some sort of damage which seems to be a working alternative to having an AD+Armour item atm.
