Because most league players don't actually develop a system. They play on auto-pilot.
You have to be self conscious of your own play and be cognitively active as much as possible throughout a game.
It's extremely easy to just switch on auto-pilot, without even being aware really.
There is a lot of information out there on how to better yourself as a player, but you can't say for sure that everyone who reads or comes across that piece of information will utilize it to its fullest or even remember to apply, and just kick on auto-pilot again.
In my opinion, the best way to spot consistency in lower level play is a new difference in Gank avoidance / Map awareness ( top tp, mid roam, jg last seen )
Death frequency lowered, and having a solid plan on progressing throughout the game to apply pressure on the map.
The difference between a Bronze Silver to Gold Plat could very well just be how effective the players can utilize information and consistently think about the current game, rather than just CSing and Moving to mid bot top dragon baron.
Someone with a logically sound plan vs someone who's auto-pilot. The logically sound planner will always be in the lead, compared to auto-pilot who's completely blind simply cause they aren't using their brain.