I love what GOG is about, and I myself have a bunch of games on there, but given that most people's friends are on Steam, unless a game offers crossplay, nobody is going to switch and lose out on time with friends. While they're there, it follows that people would also buy and play their single-player games, so their libraries aren't split.

I'd love to see GOG have a bigger influence, but there needs to be an easier path than "just abandon Steam."