Imagine if the NFL changed rules every two weeks to keep things fresh. People get pissed off at good (or bad) tweaks to CS:GO and those tweaks can make for very different games. Riot still has an incentive to make money short term over building something that will be around in twenty years. Unsolvable? Maybe. But whatever Riot is working on now won't be what they are in five years.

I guess what drove that statement was the StarCraft -> StarCraft 2 transition, both of which are shadows of their former selves because the business model of a game publisher is not that of a sports league. They have conflicting needs.