Lots of Tank threads, one obvious reason

Instead of replying to all these threads that are wondering why tanks can't tank, I'll make one to explain the reason: #Tank items were nerfed.

Unlike every other class update, where most champions of the class were changed and their items were buffed, Riot didn't want to make the same mistake. So they went the complete opposite direction and only changed 3 champions to suit their new weaker item changes. That means the rest of the tanks (read: the top lane tanks), got completely screwed over.

Their stated goal with the items was to make it so that you are less effective against the opposite damage type from the defense you buy. So armor/MR was increased while health was reduced, since health is defense against both. That had the additional adverse effect of nerfing each champion's abilities instead of just their defenses, since most of them scale HP for shields and/or damage. But, again, only 3 champions were changed to suit these new items. A few of the rest received small buffs that in no way compensate for what was lost (ex. Poppy gained +2% damage on her Q even though tanks lost over 10% of their available HP).

#Then three additional problems were introduced:

1. ADC items: Bork had some AS switched to AD, so ADCs became more suited to fight higher armor enemies. Major crit items had their costs reduced to compete with lethality builds--which weren't nerfed.
2. Support items: Buffed and changed. So add around 1000 effective health to any squishy target if they have an enchanter, on top of whatever lifesteal they buy on their own.

#And #3. New Runes The new runes added a heap of damage to the game, but the only defense options you have don't stack up to the old runes. On the plus side, damage was even added to tank runes. But that doesn't help you do your job of surviving long enough to get several ability rotations to CC the enemies.