Tanks, like every other class, are part of the balance system. They struggle right now, but this post is about the consequences rather than why.
Champions can be categorized roughly into laning champs like Renekton, Zed, or Jhin and scaling champs like Camille, Orianna, and Jinx. Laning champions want to win lane, snowball their advantage, and end the game before the enemy team groups around its tanks. Their hard crowd control and cheap bulk make leads less relevant, especially against compositions based around melee or burst. A fed team is dead if caught or useless if zoned by a tank.
When tanks are uncommon, teams can draft melee, burst, and laning champions without ‘falling off’ later. They can recover or continue to snowball by finding picks, unobstructed by tanks. Meanwhile, ranged, utility, and scaling champions never ‘outscale,’ since they cannot hide behind their own tanks. The meta will therefore comprise assassins, duelists, divers, and juggernauts, alongside ‘safe’ or ‘bully’ Midlane and Botlane champions like Lissandra or Ezreal. They can survive or win lane by design and peel or escape for themselves later, while also having enough burst threat to ward off their meta opponents.
We need Top and Jungle to have viable tanks to increase the chance that a team will draft one, correcting the meta.