Why are not more people using Google Hangout ?
It has more features than Whats App, everyone (with Android) has a google account so you just need to install it and you can use it on every PC/Mac.
In my opinion 10x better than Whats App.
https://play.google.com/store/apps/details?id=com.google.android.talk&hl=de
I totally agree with you!
Hangouts offers a better privacy too than other 3rd party apps and you don't need more than your google account.
I don't think that Whats App offers group video call of 5 persons in witch one person is from tablet and the others are on Linux, Windows, OSx and iOS of course.
My guess is that What's App has got it's approval of coolness and popularity from teenagers.
I for one, try to encourage my friends and acquaintances to try hangouts.