The dominance of Valve Software’s digital distribution platform Steam rarely gets challenged. Back in 2009 it was estimated that Steam enjoyed around 70 percent of the digital distribution market in terms of dollars generated per month, and the service certainly hasn’t grown any smaller since. Valve makes big money in PC-centric markets like Germany and Russia, and these successes underscore how influential and important Steam is in the PC sector of the video game industry.
For independent developers who lack the budget to run effective marketing campaigns, whether or not people can discover their game is a huge concern. This makes Steam extremely attractive to indies.
There are plenty of other ways for indie developers to distribute their games like selling off their own websites or working with other digital distribution services, but nothing beats having space on a platform like Steam which is hugely successful and popular.