Can you explain why you guys have a tendency to ignore our plea of buffing weak champions to be on par with the strong champions instead of just nerfing the strong ones to be on par with the weak ones? For example, nerfing Sivir instead of buffing weaker ADC's. Why is it always nerf to balance

All things being equal, we prefer to buff champions rather than nerf then, because we know that goes down better with players. Sometimes that's not feasible, particularly if the nerf touches one champion but you have to buff many others to have the same effect. That second situation can cause unintended bugs or even additional balance problems, and we are often operating on short time schedules to get a fix out in the next patch or two, so minimizing the number of changes is a good idea.
There are also some champions that lack counterplay or a strategic identity (some way to distinguish them from similar champions) and in those cases we think players might be more frustrated and have less fun if we make them competitive without overhauling their kits. These are the kind of champions that we love to hit with champion updates.