100% conversion rate with those you can apply sufficient pressure on, perhaps. Who'd want to lose contact with a son, brother, father over something like that? But it's a hassle, even if you don't see it that way.
Over the years I myself have been converted to Signal, Telegram (encrypted chats), Threema, some kind of encrypted IRC and OTR on at least two other messengers, Google Wave, Google Talk, Viber, ... can't remember them all. I have no idea anymore what person prefers which app and since most of those people weren't the very best of friends, contact to almost all of them has effectively ceased (in part because those specific people don't often start conversations themselves), which is a pity, but it's simply really bothersome to cater to everyone's preferences, and I absolutely can't and won't switch to $other_app fully myself, because I really value being able to talk to all my acquaintances and friends and relatives and being able to stay in touch with new ones easily and frictionlessly, and pretty much everyone is on Whatsapp, and all I need is a phone number.
If some people categorically don't value other people who don't use their preferred app, that totally weirds me out. Their choice, but not one I'm willing to make, especially since that notion of freedom I gain feels like a very, very abstract kind of freedom in a world where billions use Whatsapp for next to anything and all sorts of devices, apps and websites from all sorts of brands and sources phone home lots and lots of data, which also means eschewing Whatsapp doesn't matter a thing unless I make dozens of other painfull choices like opting out of all mainstream social media, complex privacy-centric browser setups that need constant attention to not fall behind, no mainstream phone (possibly no smartphone at all), no smart devices at all, Linux exclusively, etc. pp., otherwise I'll just leak data like a sieve elsewhere. Given that I gain what feels like very little, life just feels too short for this.