Please someone explain to me why?

Why is riot buffing ADCs BUT ALSO nerfing tanks/bruisers at the same time O.o...

MoM was a good item the way it was imo, the change is kinda strange (to the passive) but either way its fine. Trinity is good atm the way it is, but I dont mind trading the AP for CDR (even though it helps Corki/Jax/Irelia and mix damage champions) Brutilizer is a great item now Why would you increase the price of Frozen heart AGAIN (after all the ADC/Item buff) You increase the price of BC by 500 for more 15 AD... but 100 less HP (imo this is a nerf, but each to their own opinion). Even though it is strong the way it is right now. Also increasing the price of essentially all AD/Bruiser type item (Titanic/Hydra/BlackCleaver). And not to mention that you can only buy one type of potion is kinda weird to me :/. The sightstone change will have some getting used to but its a fine change to me. ER is overloaded and pretty strong, like it gives too much mana sustain then actually needed for most ADC (except for ADCasters). Death dance is a great item.

I know they are strong atm, but theres no reason to just nerf them. Buffing the ADC class was good enough to suffice :/I main top and dont really like the item changes to them, even the LW change confuse me. It is +40% bonus armor penetration, so basically if you have no armor penetration, you have no armor penetration.. O.o. LW was a good borderline OP item, but it was needed for ADC to kill tanks (the upgrade to those item was a nice change though, but I think you should have made an entirely new item for them instead).

With this change I might just play Zed/Tryn (new PD OP for splitpushers)/ AP champions instead.

Corki change is pretty lackluster imo as well, you get this awesome rocket but can only be used once everytime he goes back to base. And his damage went down because the true damage is now gone :/. I dont think it was worth it imo since the true damage was pretty big. Corki was the one champion I didnt think needed changes.

Grave is pretty cool and unique now, Quinn is awesome, Caitlyn is great and I think MF is just decent :/. Kog is super cool now but that damage reduction though haha.. he just seems clunky now imo but he was the one champion I didnt play yet so I have no right to say anything about it.

And last thing that gets to me alittle bit is how weak the offensive mastery is if you dont go into fully. You have strange mastery in there too (each unique kill will give you 1% more damage) sounds good, but its strange you wont get much if you dont kill more than 3 unique kill (which can be 20-25mins into the game depending how fast the game is going, and the damage doesnt really ramp up if you dont have the damage to make the difference. The Keystone are decent but imo they could have done much better.