Steam utilizes a business model that includes DRM integrated into the games that you purchase on their platform. What this means is you don't actually "own" any of the games you buy from Steam, but rather, you are buying a license, and is the same reason you are required to open the game with Steam. For the common consumer, this doesn't seem like a bad thing when you exchange it for ease of access to a large library of games, and the ability to utilize the social aspects of Steam, such as item and card trading, the community hub, guides, and discussions. However, with waning competition, this is communicating a very bad message to Steam that this sort of business model is okay, as DRM leads to issues with video game preservation, lack of control on the users behalf, and greedy business practices.
DRM (Digital Rights Management), is a form of control used by software publishers that attempts to prevent games from being shared and manipulated. In theory, it helps developers and ensures only the purchasee uses the software. In reality, though, it just becomes an obstacle for people who want to play games.