League's meta is almost solely determined by balance.
For example, if Irelia became meta, we wouldn't suddenly have a resurgence of Singed/Volibear games. We wouldn't suddenly have ranged top laners stop being picked and have it pretty much end up Irelia, Darius, Illaoi, Riven, Fiora, Malphite, Poppy. We wouldn't end up seeing Poppy support in order to protect the carry against her. This is all what would naturally happen if Riot properly managed their game.
Instead, Riot would nerf Irelia, while ranged top laners would continue to get played and dominate the above mentioned picks. Because Riot doesn't want to address ranged vs melee dynamics, nothing would get done about this.
That is a problematic balance regime.
Champions that are successful at something should not be nerfed solely because they accomplish what they're supposed to and ADCs can't just right click to counter it.
However, in League, that's what happens. ADCs have a hard time? Nerf what's giving them a hard time or buff ADCs. The meta that comes up revolves entirely around those nerfs as opposed to what's likely to happen in-game.
Another example? Marksman update. Keep in mind that Riot stated it was supposed to be power-neutral.
ADCs rampant everywhere from top lane to jungle, to even mid. People start picking Rammus/Malphite top; a logical answer to the meta. Riot's poor ADCs had a hard time picking 3+ AD comps into them, so they nerfed Rammus/Malphite for doing what they're supposed to do. It took them several patches to realize that the reworked ADs were the issue that caused the massive meta-shift in the first place.
What they should have done is naturally let AP tops start taking over to shut down Rammus/Malphite. That would be a metagame that did not revolve around game balance.