Do you play as often as you used to ?
Back when i was leveling up i used to play 25-30 games on a daily 10-12 hours straight but a couple of years later now in the present i just play like 3 or 4 and im talking on ARAM, recently i stopped playing SR it just got so boring and repetitive i mean that was just bound to happen sometime, game modes reel me back in but they dont last and when they are gone they are gone for 3 months they need to make a new map so that there can be some variety.
PS: Dont get me wrong i still love this game and i have supported it (and i will again when the ultimate skin comes out)