Yeah. It rode on the "free SMS" wave for way too long and people still use it because of that... nevermind that SMS-es are free in most of the world nowadays. :D Or the fact that literally every messenger is free and most have no ads (unlike Viber which does have ads).
The very continued existence of Viber is a living testament of the glacial pace with which the non-tech folk pick up on what's wrong with some of the popular tech.
I actually think the existence of Viber is a testament to how much Western tech does not pay attention to parts of the world like Asia.
I genuinely hate the UX of Viber but since moving back to the Philippines, I've been involved in this long lesson on how much tech orgs (at least in the US) don't pay attention to these parts of the world. It seems to me that lack of care and attention leads to the rise and dominance of companies like Viber, Grab, Lazada, and their ilk in markets like the Philippines.
In the end, these apps that you and I both despise are what works best for the consumers that use them most precisely because they just work (but not well).
I like how practical a lot of Asians are. This gave rise to WeChat where you can literally do almost anything you can think of -- calling for transport and paying people included.
This made it really easy for the Chinese gov to track people but in the end people value convenience more than potential surveillance state repercussions.
We as a programmers must learn to respect that and think in terms of what's convenient for our users -- and not what's a trendy tech or some such.