User blog comment:Odisseas25/Why does the AP go to mid?/@comment-69.206.240.248-20130210031813/@comment-69.206.240.248-20130210032001

tl;dr 2v1 is harder than a 2v2 or a 1v1 and lane swapping is risky, meaning that while it gives you an advantage in one lane, it gives you a disadvantage in another, making it rather risky. In other words, it can work very well for your team but also may potentially go very badly.

Meta has also been shaped this way because it has been found to be most effective time and time again.