RNG is RNG.
The RNG at lower ranks is even more pronouced. Because low ranks are not complete players they might be pretty good in some areas but complete trash in others.
There are mechanically skilled players that always win lane then keep diving in 1 v 5 and running off alone instead of getting obectives. Sometimes you have players that postion well but can't farm and couldn't hit a skill shot to save thier lives.
Some players make good game calls, but why would you listern to them if they have been feeding all game.
Then at lower ranks, idealy you want a mix of these players. But everyone is at the same rank but with completely different skill sets... well different skills sets can be fine... when you all have the same skill set that is when it is terrible.
You all win your lane then have no idea how to take objectives and push to win.. so you throw.
All they all fail in lane, they might be good later in the game but you get snowballed out of the game.
I had an insane game when I was in silver 2, where my adc and mid laner were first time in ranked players... my adc had 14 farm at 15 min... 14! less than a cs a min. The mid laner also obviously fed.