That's not really apples to apples though. Gmail worked with external SMTP services to send and receive mail. Google+ required that anyone you wanted to connect to also have been offered and accepted an invite (or received one of your limited invites).

It seems plausible that social networks have more of a network effect than things like a game streaming platform. Obviously there's still some network effect and a certain marketing aspect to it, but I don't think they're directly comparable.

You have to convince game developers to port their games. If the reward is a few thousand users, it's going to be a hard sell. Also the R&D and infrastructure required to even start up the project is too high. Building a Gmail (especially back then) is small potatoes in comparison.