[r3bl]

It's a simple problem of where the market is.

India, Russia, and Brazil isn't the target market for people like Schneier. If you narrow the market to the US, Statista reports that Telegram has twice as many users in the US as Viber.

I'm from one of those countries where Viber is hugely popular (by far more popular than WhatsApp and Telegram), and I hate it with passion. Kind of like Telegram, its end-to-end encryption was also home-made last time I've checked, but at least it's turned on by default.