Why is P5 ~ P1 full and trash players and makes it impossible to climb?

http://na.op.gg/summoner/userName=train+to+dead

I literally had 60%+ win rate when I was 80 games total and I got to diamond 5 in no time. Probably like most people, knowing how trash p1 and d5 is they just wanted to reach diamond and do monthly maintenance until season end to get the banner so I did the same. However I lost a lot of games when I tried to get to d5 with 50 LP so then I can stay off ranked for the rest of season. I Dropped all the way to 45% win rate and the mmr gets so much worse, and I was losing 20LP per game winning 15LP. It's funny how riot quene you up with absolutely trash people when your mmr is below where you should be. I keep getting people from plat 3 below sometimes gold and one time even a fucking silver 1. As a jg/mid main I watch the map all the time and all I see is people keep doing dumb shit mistakes; pushing in without wards, facecheck bushes and ash global ults trying to snatch a kill or even if it landed, it wouldn't grant a kill.

Now I play solo mostly and now i'm thinking to start doing dynamics as it's just almost impossible to play solo with continuous shit players on my team.

Yes I'm pretty salty with how my games have been going, but seriously fuck man, A LOT OF TRASH KIDS at my elo.

done ranting, anyone wanna carry my ass please let me know.

have a nice day.