Someone wanna explain why matchmaking is so terrible in Placement games?

Every single game i play in ranked i get someone that feeds. And my solo laners never know anything about the game. I literally knew we were gonna lose when my top picked teemo. Teemo and our mid Cass proceed to feed all game. The score was 7 to 21 at one point. No one person did anything to win that game. They won the second the game started and they were given better players. Yeah whatever i couldve played like a god or whatever people will say and carried myself. But you tell me wtf to do when all your lanes are pushing onto towers and your solo laners are just feeding. I get waaaaaaay better team mates in norms. Ranked is honestly a sick joke at this point because i know im just gonna get trolled. Why are the teams NEVER even