Riot would probably never outright delete the lore, because a good portion of the fanbase actually likes it, and would probably outright move to some other game if they were stupid enough to get rid of that demographic's draw-in. Crappy lore is better than no lore at all, if barely, but a bit of complaining is better for Riot than having part of their income vanish into the ether.
Lore exists to make champions more than just a soulless collection of skills. Lore gives a champion character, which the player may then identify with, and if they like the character enough to keep playing, then they keep making Riot money. Without lore, champions of all sorts are pretty much indistinguishable from the bland and lifeless player avatars of CoD and Battlefield, with nothing to differentiate one from another apart from skills, and really, the community is toxic enough without drawing in that crowd.
So the lore's actually quite a bit more important than you've implied, because the lore and the game are really the only two components of League of Legends, and without lore for flavor, there's no fun in playing apart from the hyper-competitive type of "fun" which is responsible for the "omfg u [expletive] suck [expletive] gtfo [expletive]" toxicity which Riot is trying to crack down on, and which the online FPS community is infamous for.