Well, Riot as a company has to make sure it survives. Drawing viewers will help the game survive. We trash on Riot all the time but a free to play game has to have some way of making money. That's why they make skins, and hextech crafting, other things to pay for, etc. So when they make ANOTHER Lux skin, it's for money. However, they genuinely do try to make the game fun to play. They give you watch rewards and stuff because there's a GIANT FANBASE for it, and having a pro scene is healthy for the game's lifespan. They want to satisfy the viewerbase, and also give missions for people to search out and do. Missions are typically a fun thing and they want to encourage watching the pro scene. It's not like they don't want you to play the game, but they are encouraging watching as well.
Edit: Making money as a company is not a bad thing. If they are trying to use that money to go into other things, such as branching out or advertising, paying their employees and hiring more people to get a better game out there, with more exciting new champions or reworks, balancing, etc. They are trying their hardest, even though a lot of people shit on them. And I'm gonna get shit on for this post with downvotes of people who simply thing "grrr Riot bad company >:(", but the truth of the matter is that all of those people who downvote with no response know that I'm right. lol. But if you wanna discuss this, go ahead, type some shit out, I'll read it and we can discuss!