Easy: End to end encryption that’s not controlled by Meta.
It could take a while, but look at all the social media messaging apps from the past: ICQ, MSN, Yahoo, My Space, GChat, Orkut, Tumblr, Snapchat, FB messages etc
They come and go. I sure don’t know what the ultimate chat/social media app looks like.
None of those services had even a fraction of the market penetration that WhatsApp has (in Europe and basically most places that are not North America.)
WhatsApp is used by teenagers, great-grandparents, businesses, everyone. When you give someone your number in Europe, they won't ask how to contact you, they will just send you a message on WhatsApp 100% of the time. Only tech nerds and small groups use Signal etc.
To be clear, I don't think this is a good thing. But it is simply the reality of the world. It's been like this for 10 years with no signs of changing. WhatsApp could of course die one day, but only if Meta does something categorically stupid or unpopular that forces people off the platform (eg, what Twitter is doing).
WhatsApp is not a social media platform and that's precisely why it is so universally used.
My 3 kids are teenagers. They don't use WhatsApp. They use iMessage or group chats on Instagram. No one I know uses WhatsApp, well they've never asked me for a WhatsApp username.
It could take a while, but look at all the social media messaging apps from the past: ICQ, MSN, Yahoo, My Space, GChat, Orkut, Tumblr, Snapchat, FB messages etc
They come and go. I sure don’t know what the ultimate chat/social media app looks like.