Everything is competing with each other. Stores with other stores. Games with other games. All that's happening here is Steam won't be quite so absurdly rich, and more devs will have more of the revenue from their game sales, which means more devs, more content, etc. And that means more competition. I seriously doubt that's going to stop now.
Could also lead to fewer discounts which leads to less sales, which leads to less revenue, which leads to less devs, which leads to less games.