You're making just the exact same mistake my comment referred to. The 'joke' is that it's just Google employees, but guess what? Reality doesn't mirror that. My circles are full of people who aren't Google employees. If yours are, then either you work at Google or you have a weird selection of friends and associates.

If you have proof that the 170million odd members are predominantly Google employees (which seems unlikely, unless they've spent their 20% time developing AI to be used as social networking bots), then I'll be pleased to see it.