because steam has lots of them :-)
Steam is a digital distribution, digital rights management, multiplayer and communications platform developed by Valve Corporation. It is used to distribute games and related media online, from small independent developers to larger software houses; in October 2012, Valve expanded the service to include non-gaming software. Steam provides the user with installation and automatic management of software across multiple computers, community features such as friends lists and groups, cloud saving, and in-game voice and chat functionality. The software provides a freely available application programming interface, Steamworks, that developers can take advantage of to integrate many of Steam's functions within their software products, including copy protection, networking and matchmaking, in-game achievements and micro-transactions, and support for user-created content through Steam Workshop.

because steam has lots of them :-)
Steam is a digital distribution, digital rights management, multiplayer and communications platform developed by Valve Corporation. It is used to distribute games and related media online, from small independent developers to larger software houses; in October 2012, Valve expanded the service to include non-gaming software. Steam provides the user with installation and automatic management of software across multiple computers, community features such as friends lists and groups, cloud saving, and in-game voice and chat functionality. The software provides a freely available application programming interface, Steamworks, that developers can take advantage of to integrate many of Steam's functions within their software products, including copy protection, networking and matchmaking, in-game achievements and micro-transactions, and support for user-created content through Steam Workshop.