Because 90% of the time the thread starts off along the lines of "I always do well in lane, but my teammates always feed."
Reality check: you don't ALWAYS win your lane, and your teammates don't ALWAYS feed. This just doesn't happen, even in diamond where people are actually good. The tallest barrier preventing you from getting out of low elo is your attitude. If you take the attitude of "I'm good, really, it's just my team holding me back" then you'll be bronze forever, guaranteed.
There will be times when you will lose lane; sometimes you will be slightly behind, sometimes you will fail miserably. No one wins lane 100% of the time, and even if they did, winning lane =/= winning the game. The sooner you begin to accept the fact that you are capable of making mistakes (and more importantly, that you WILL make mistakes in EVERY game you play), the sooner you will be on your way to getting out of bronze. The people who actually climb are the people who don't deflect responsibility and blame onto their team. They own up to their faults and admit they need to improve.
In fact I would even go so far as to say that the players who make mistakes learn more than the players who play well all the time. If you're not making any mistakes, then you are blinded by a false confidence in your own ability, which delays the learning process. The more mistakes you make early on, the greater the opportunities to figure out what went wrong, how to fix it, and how to adapt if the situation ever arises in the future.
I'm not saying to go out there and deliberately throw your lane assuming you'll get better. What I'm saying is learn to recognize when you've won and when you've lost, and the deciding factors that led up to that outcome. Does the enemy have more cs than you? Whose tower fell first? Did either of you get kills/assists on each other? It's also important to note how often the enemy laner leaves to help other areas of the map. A won lane does not necessarily have to occur strictly within that lane. A laner who has great influence on other lanes will win his own lane indirectly due to the gold and objective advantage secured by roaming. Doing this will also help with those ever-prevalent "feeding teammates" by keeping them from falling behind.
Bottom line here is: don't be so sure of yourself. A little humility and objective analysis of self-worth will go a long way when attempting to climb.