Part of the reason is likely because you have a 43% win rate in your current division. The game is trying to balance you into a division you will have more success in. If you start winning more games than you lose your lp gain rate will increase and your lp loss will decrease as the game tries to move you into a division or league that is more suitable to your skill level.
Basically if you want to climb the ladder play champs your have a higher win rate with. I looked you up on na.op.gg. I noticed you have a win rate of 50% or better on azir and talon. If I were you I would just play those 2 champs to climb. Avoid Darius, even though I see you like playing him, but your win rate over the last 2 seasons is ~30%. Playing him will more likely make you slide backwards. Queue up for mid as primary (play azir and talon) and find a secondary role and a couple champs you have success playing with.
Place less focus on lp gains and losses. Steadily improving your play, and picking champs you have success on will show results