I live in the US, why should I install Whatsapp? It's annoying that I need to install so many apps just to do the same thing which is chat with people. I care about simplicity, it's inefficient and a waste to have 3 apps that do the same thing. This is why I never installed Whatsapp, or Line, or wechat, or FB Messenger.
I want all my messages to be in the same spot. Not 4 different applications. It just so happens, that the Messages app is installed by default on my phone, therefore I know I can receive SMS as well as iMessages. That's all I need.
Google should get their sh** together with RCS and come up with a default app. "install whatsapp" is not a solution.
Well if you don't care to speak to people with android in a modern way sure no need to install.
That is good reason enough.