The problem with replacing e-mail is that e-mail works well enough.
Other hypothetically “superior” replacements come and go (Google Wave, Yammer, Jive) - some are sticking around in limited scopes (Slack / Teams) - but none have displaced e-mail completely. You always have to ask: “Are you on Teams/Facebook/X?” some people are, some people aren’t. Just about everyone at least has e-mail access, and uses it to some degree or another - if nothing else to verify identity for accounts on other services.
The problem with replacing e-mail is that e-mail works well enough.
Other hypothetically “superior” replacements come and go (Google Wave, Yammer, Jive) - some are sticking around in limited scopes (Slack / Teams) - but none have displaced e-mail completely. You always have to ask: “Are you on Teams/Facebook/X?” some people are, some people aren’t. Just about everyone at least has e-mail access, and uses it to some degree or another - if nothing else to verify identity for accounts on other services.