It's not just a "this is a business" thing. Riot providing you with a service! And one, by your enthusiasm, I would think you appreciated. I don't understand all these posts complaining about paying some money for a product I, personally, have sunk WAY more hours into than most 50-60 dollar games.
And it isn't the end of the world if you don't own all the champs. Free champ rotations ensure that you can try people out periodically, and you can spend that ip where you want the champ most. And if you can't stand the wait, then that's great. You're supporting their business and helping us all continue to enjoy LoL.
Now, to explore the flip side, imagine that champs dropped quickly enough for most players to own most of the champions. Riot's profits drastically drop in that scenario, which I wouldn't wish on them. I want them to continue to see success, not only because they deserve it for making such an awesome product, but so that other companies will see what it takes to be appreciated by the public.
The more money we make for LoL, the more other companies will pay attention to the way they update their game, treat their players, etc. This is a good thing for gamers. Even if we had the power to strip Riot of their profits, it would be shooting ourselves in the foot, as gamers, to do so.