Teammate ranked Platinum, with the Bronze Mindset

How is it that someone who never looks at the minimap, chases kills from one side of the jungle to the other, but farms like a champ can get into Platinum but someone that is actually trying despite terrible matchups and just a couple bad days of League can't get past Silver? Granted, my mechanics and mindset aren't always the best or in the right place, but I am trying to not be toxic.

Sorry, just ranting.