Why has LOL always been so laggy?

I know this question has been brought up many many times before but what is it that causes the infamous league of lag? Most people seem to be able to play other online games fine with 0 lag*.** I am talking about nationwide here**, is it because of the lousy NA internet infrastructure? but the lag seems to affect LOL the heaviest. Is it the huge player base? but the lag is here at all times of the day whether it is midnight on a schoolnight or noon on Saturday the game is still slow as heck. Is it the servers on Riots end? We just had a server move to the new Chicago server. So any definitive answers about this or are we all in the dark?

*At least according to the boards, whether or not this statement is true is debatable, but I myself can play other games without lag