Where I come from (Malawi, Africa), WhatsApp is so widespread that most people prefer it over email - to the extent that people don't really check their e-mails unless it's required for work or they are applying for something. For most people, WhatsApp is the de-facto communication channel.

I help moderate a community of developers and we hit the whatsapp group limit of 1024 members and sometimes have to wait for someone to leave (intentionally or accidentally) before we can add new members. We've tried to move people onto "better" platforms like Discord or Slack but we always end up coming back to WhatsApp which is subsidized via MNOs (mobile network operators) social media data/internet bundles and for the fact that most people are just stuck on whatsapp.