Why are there multiple magic resist + AD items, and only like 1 armor + AP item?

A few reasons:

Many AP items have HP attached to them.

Adding more AP/Armor items also makes it possible for tanks to abuse these items since many of them now rely on inherent %damage reduction or inherent defensive tools in general.

While there are multiple AD items with MR, it’s incredibly inefficient to build more than one. An ADC doing this would, in most cases, be sacrificing a great deal of damage.

Mages also can build void staff, which ignores almost half of the enemies MR with 40% pen. Meanwhile, LDR and MR do 35% and 25% respectively. This is also because the nature of pen and damage type: 40% pen on burst champions is far more lethal than 35% pen on DPS champions (but the AD% pen scales much better since DPS works vs several targets and burst typically only works against one - this is the very nature of AP vs AD).

AP also scales shields and heals, whereas AD doesn’t necessarily. That said, there are AD champions that have AD scaling shields and AD does scale lifesteal, but this is only in individual cases where it benefits the champion building it. Supports and many Utility mages can scale these shields/heals on themselves or allies. This would make additional AP/armor items contribute more to mage tankiness.

Mages have longer range than ADCs and the shorter ranged mages have inherent tools to offset their range, or the short range is an intended weakness. Because of this, the idea is that diving mages is supposed to be how you deal with them because of their long range. Giving them additional durability options when they already have tons of HP/AP items while also having banshees + zhonyas makes that a scary proposition for further empowering mages teamfight.

These are the reasons why. Are they justified? I don’t know, I lean towards yes because of the fact that tank MR stats suck as well and clearly riot intended these aforementioned things to be a weakness for mages. I think we all realize what the problem is this: mages don’t have ways to itemize against AD in lane, which is a fair complaint. While I think mages struggling vs AD in lane is also probably an ideal balance, the reality is the scale is tipped way too far in favor of ADs. I think what could help a great deal is buffing seekers in such a way that really helps deal with AD - perhaps giving it full armor upfront or giving more AP (let’s say it builds from two cloths and blasting wand) so it doesn’t feel like it cripples damage so badly. I actually do think adding an additional AP/Armor item isn’t a good idea for what it’s worth. I’d also say hexdrinker should become an active rather than be a passive so that it actually requires skill to use rather than just prevent you from burst execution. Obviously further changes would need to be made to it but that’s another discussion.

AD bias. ADs always had superior items.

Because:

1. The active on Zhonya's is pretty much universally applicable.

2. Between the 45 armor from Zhonya, 60 MR from Banshee's, and the HP you can get from Morello, Liandry's, RoA, and/or Rylai's, a mage can get pretty beefy with multiple defensive actives/passives.

3. Most fighters aren't gonna build QSS. Most carries aren't gonna build Maw. Almost no one is going to build both.

Because building together will almost never happen, but multiple armor AP items would be bought almost every single game in lower elos, since I'm almost always playing against 2-4 assassins.

I mean, there was a point where mages would literally build frozen heart.

one day...

Because Riot gave a number of AP items more HP.

It's bullshit but thats how it is.

...2. There are two Magic Resist+AD items on Summoner's Rift. And nobody builds them together.

This is just a dishonest post.

###Asking the real questions

But in all honesty, no idea. I guess in Riot's point of view Zhonya somehow overcomes in power against both Mercurial Scimitar and Maw of Malmortius.

why is there one single item that gives AD and armor ? and it's a garbage item too

Because there are more archetypes of AD champion than there is of AP. AD champions include everything from marksmen to fighters who also have archetypes of their own.

While most AP champions are usually mages, a few ap assassins and a handful AP bruisers which i guess we call battle mages now.

AD items need to fill more niches and roles than AP items do.

Because mages werent made to be bruisers that deal insane ap damage with tankyness? Why dont AD champions get a that increases our AD by a huge amount? Are you seriously suggesting a 700 AP mage with 300 Armor would be balanced? Not only that, but the mage also gets huge health from Morello, Rylais and Liandrys. So youre technically speaking, if you want armor + ap on your precious mages, youd need to give up tons of your AP. No more 100 AP on items, no more Rab, youre now going to have about 300 ap full build instead of 800-1000.

multiple is a bit exaggerated for 2, and ther also is only 1 ad+armor item.

I really wouldn't mind more ap/armor options, especially some that actually focuses on armor+ap rather than an incredible potent active. However, saying ad's have multiple(2) mr items is very poor reasoning for it...

Ability power + Armor Attack power + MR

and for shits and giggles we'll say for attack power + HP with Archangel's being the honary mention like Death's Dance it.

AD gets 1 more MR + AD option, AP gets 1 more AP + Health option.