For most people it's far easier to just install an app instead of going through a whole setup and registration process and remembering a login handle and a password. I have a lot non-geek friends who are happy with how WhatsApp works. They mostly ignore all privacy issues with this.
I'm not really directing this critique to WhatsApp users, rather to WhatsApp authors, who exploit users' comfort of no configuration vs one time configuration / registration, while causing with that a proliferation of walled networks. They are not doing a good service to users at large.
One time configuration / registration is not really a burden. All users are familial with that process. And they don't do it each time they read their e-mail for example. As I said, the negative impact of non interoperability proliferation is way more significant.
