No, Steam is a game market place and library. People who buy their games on Steam are beholden to it being available on their Steam library. When you own a game on Steam, it is installed on your machine and runs on your machine but you must use the Steam Client to run it.
Many people have large libraries of games on Steam. As a hook, Steam allows me to distribute keys to the game in cases like the kickstarter or an itch.io purchase. I am sure they are hoping you buy some of their Steam dependent products. Many developers only release on Steam. I have chosen to allow a DRM free version which you are using.
Beyond the automatic updates, Steam has an API which offers various other things for your game, which with code I could plug into. Like external achievements and a workshop which handles the sharing of things like maps automatically, and even "Trading Cards".. Also an interesting hook because then the program is beginning to only be able to run on Steam to do "cool stuff" with these features.