Why do people think armor itemization is bad?

There is 2 reasons Armor feel bad:

MR items gives way more resistance 70 mr+burst negation passive+500 health almost as much AP as morello and 50MR + magic pen aura gives MR to legit all your team and a usefull active and cdr and health 500 hp 70 mr way too much healings and cdr

Armor penetration is everywhere, from the masteries to the items 20 flat armor pen up to 30% armor shred 10 flat armor pen 10 flat armor pen 45% bonus armor pen

Here let's take a look at the magic resist penetration options

35% mr pen 15 flat mr pen 20 flat mr pen

So in total, ADs can get 30 flat pen+ 30% armor shred + 45% bonus armor pen While APs can get a maximum of 35 flat pen and 35% magic pen.

What are the armor options?

wich is kinda useless since the nerf because it just doesn't deal that much damage unless you are is good, but it got nerfed too and the aura can't even be compared to locket's. Also lacks an active stats are ok but the passive isn't as usefull as spirit visage or banshee and the active doesn't compensate for that got it's nice passive nerfed and price augmented since it was leggit the ONLY armor item that was equivalent to magic resist options and that felt right when buying is just a less good dead man plate, less damage, no CC. only gives some armor and utility stats since they nerfed it (no more AP). Could've been the equivalent of abyssal, with an AOE passive and some AP+defense but nah. is worth 5 armor against assassins since they will all get wich is 40 flat pen. And riot isn't even considering lowering the price because the active is too strong according to them. have cool passives but 50 armor is almost worth nothing with all the armor pen available is rarely bought on anyone

TL;DR: MR options give better stats and passives/actives than armor options: and armor pen is omnipresent making armor feel weak.