<< LINK REMOVED >><< LINK REMOVED >> Because Steam realistically pretty much has the monopoly on digital PC game sales. Sure, there are alternatives (GOG, Desura, Origin, UPlay), but if they combined have more than 10% of the market, I'd be amazed (I'm not counting companies like greenmangaming who just sell Steam keys). Realistically, Steam has become so ingrained as the top dog, it can't be displaced unless they changed how they operate in order to deliberately scare people off.
Those that vote for EA really should grow up. I don't like them much as they swallowed up a couple of my favourite developers back in the day, but I wouldn't place them in my bottom 100 companies, let alone the very bottom.