Why is this matchmaking a thing?

the account you make this post on isnt even in the game implying you were smurfing there is only one player that stands out as a smurf being the leesin so im going to assume that is you, your main account is plat 3 its clear looking at past games the leesin has high mmr being as every rank game is a tier average of gold if you look at the enemy team one of the plat players has a negative winrate while the other is just shy of going negative one is also duo'd with one of the gold players.

matchmaking isnt perfect but smurfs and duos dont help it they create weird situations but come on we all know the leesin isnt a silver player, if you want to buy accounts and smurf dont complain when you lose games

If the individual persons are on a losing streak, they are placed in lower MMR regardless of rank because they have been playing poorly. Matchmaking is not based on visible rank, but instead on MMR.