One needs an email address because almost every service you use on the internet requires an email address. Until this changes, we are stuck with email.
Discussion
Like Telnet, FTP, and Arpanet, email was one of the first successful internet applications, with industry standards set by RFC 822 (!?). I guess that is the reason why a lot of stuff still works using email standards. Some legacy systems are better left untouched. But since today is April Fools’ Day, we should think of something for BIPs like RFC 2549 https://datatracker.ietf.org/doc/html/rfc2549 😂