It would, but the web is a mass-market project - while it would be nice if everyone understood how to read a URL, we should cater to the lowest (within reason)

It would, but the web is a mass-market project - while it would be nice if everyone understood how to read a URL, we should cater to the lowest (within reason) common denominator - especially when it comes to security. The threat model for phone numbers is considerably different, not least due to the link-based nature of the web and email. The URL takes on the role of both the number and the caller ID (if caller ID didn't suck) - you should be able to be confident that you're talking to who you think you're talking to.