As many, many other people have stated here - beyond just burning social capital by forcing your other friends and family to use Signal (which isn't even federated), a lot of social, community, and commercial things are coordinated exclusively through WhatsApp.

https://news.ycombinator.com/item?id=25669600

https://news.ycombinator.com/item?id=25673859

https://news.ycombinator.com/item?id=25669072