Step 1: Determine whether or not changing the lore would make more money than it costs.
Step 2: If yes, then use market analysts to figure out what people in League's age group like. If no, then just forget the whole idea, and skip to step 7.
Step 3: Figure out how to retcon the lore to fit into that cliche.
Step 4: Butcher all of League's lore, make it "edgy" and make everyone more eager to throw money at Riot.
Step 5: Wonder if maybe they should actually care about their game, but then return to humping their wallet, because money is life.
Step 6: Release half-assed, boring lore that doesn't really serve any purpose other than to rehash what we already know and give the characters more broody, depressing personalities, 'cause that's what sells.
Step 7: Hump diamond-lined wallet and worry about money incessantly, because billions a year OBVIOUSLY isn't nearly enough.
Step 8: Ignore anyone who complains, 'cause money knows better.
Step 9: Release a skin loosely based on the retcon, and/or make up a "new universe" to make a skin, then never explore said universe.
Step 10: Hump wallet some more.
Step 11: Continue humping wallet.
Step 12: Repeat, but throw in more wallet humping.
Basically the process for any F2P company. The game itself doesn't really matter, just money.
Fact of the matter is: Lore doesn't make money (in an F2P game), but costs quite a bit (in today's world, anyway). So, since there's no income potential (outside of champ re-releases and skin releases), lore is not a priority at Riot in the slightest, and is on the back-back burner. They'll tease and give just enough to make lore hounds happy enough to throw money at Riot for skins, but absolutely no more than that. That's how an F2P company operates in general though, even regarding things like the core game, the client, all that: Absolute bare minimum until forced to do otherwise.