People use what they got. Most businesses accept American Express. So people carry it in their wallets. Network effect. Facebook is a good meeting point. Its hard to be pedantic on things that literally will kill minor relationships.
Well, there's an opportunity. Five years ago, everyone in China used to use qq, which is kind of like Chinese Facebook: everything public. Then wechat came out, and now I never use qq any more, I mean, noone does.
Both qq and wechat are owned by tencent.
They are. Not sure that changes my point much? The user database/registration are entirely separate. There is no lockin being circumvented by virtue of both being tencent.