In a lot of developing countries WhatsApp doesn't count against your data plan. Signal data is billed like any other app. It's not easy asking all your friends to pay for something they already get "for free".
Ripe for antitrust litigation. Reminds me of Microsoft bundling Internet Explorer. Unfortunately, developing countries have bigger things on their plate than going against Meta, especially since I figure the “bribes” and promise to improve the nation’s internet infrastructure are very substantial.