Why Moonfalir Spellblade is not in summoners rift?

Its a great defensive item overall, heres the stats: -50armor -50mr -50ap and a uniqe passive which gives 35% tenacity. But its only avalible on TT, and heres why i think it should be an SR. Mages got 3 items which gives them mr: Abysal, Athenes and Banner of Command, but the last two is mostly built on supports and not viable on mages. So most mages have one mr option, which is abysal. But my problem with it is that it reduces the mr of your enemies around you. Thats great. But long ranged/Artilery mages (like Xerath or Vel'Koz) doesnt really benefit from this, since their abilities ranges mostly out of this aura. So, for example if they are up aganst lb they doesnt have any defensive mr options, and lb is a really hard counter to them. And i know it has other stats as well, but why buy it when you are not benefiting from everything that an item gives. They also only got one item which gives them armor: Zhonyas. Its and item that is almost intant rushed aganst ad assasins, and a lot of time even agants aps. It makes you avoid dmg for 2.5 seconds which is really power full, but if you need to build armor(for example if u are up aganst a mainly ad dmg team, which happens commonly theese days) this 45 ad zhonya is your only option. And Spellblade could solve this issue. The passive of Moonfalir Spellblade is also really good aganst ap mids, becuse they often have a lot of cc. So considering the things above, it could be a nice defensive item which also give you some ap, but you wouldnt build it for that. The numbers could recieve some changes, but i think it should be on the rift.