The problem is that what makes Whatsapp sticky is the network effect. People use Whatsapp because everyone has Whatsapp.
But if you now have several millions of people who will not use Whatsapp at all, all the groups that they are in will need to migrate to the alternative (which is pretty much Signal/Telegram at this point). So those few million become few tens of millions. And once they migrate and start liking it, they may avoid Whatsapp as well, because it's far easier to just use one app, and then their groups need to migrate, and so on.
But if you now have several millions of people who will not use Whatsapp at all, all the groups that they are in will need to migrate to the alternative (which is pretty much Signal/Telegram at this point). So those few million become few tens of millions. And once they migrate and start liking it, they may avoid Whatsapp as well, because it's far easier to just use one app, and then their groups need to migrate, and so on.
Edit 1: Added Telegram as an alternative.