1) You lack the ability to think. People in bronze/silver think in 1 dimension. Its not till you hit diamond that your thinking in 3-D.
example: your team is spawning superior minions. Do you
A) force a team fight in lane with superior minions and go for win
B) try to get dragon or Baron
C)take down another lane inhibitor
D)hang out in jungle and kill random monsters
If you are in bronze-gold, you and your team mates most of the time pick D. Again, most people in that ello thinks in 1 dimension.
2) You don't do your research. You need to watch streamers, watch PRO games, and look at online builds. You also have to do test as well in VS AI to test out various things.
3) You lack the ability to work as a team. 90% of the time the reason why you lose low ranked games is because you don't group up during the late game to achieve an objective. Whether this is pushing a lane or getting an important jungle monster. You also don't communicate anything, even when people ask the team something you remain silent. A bad plan is always better than no plan.
4) You don't press the tab key and use the information that it gives you. This will tell you several things.
1)builds of your enemies
2)which enemy champ is carrying and their level
3)which of your team mates is struggling
This goes back to 1st point. When was the last time you pressed tab and thought " oh gee this champion is going this build, i should go this build to hard counter , or use this build so I dont get melted instantly".
Is your tab key broken? Because I bet you barely ever press it. And even if you do,your probably not thinking on the info that it is giving you.