It wasn't that miraculous, actually. Remember that it was invented before HTTP even existed. It was developed at a time where the only contender was Usenet. Internet was not yet used for any commercial purposes; there was no concept of platform. Internet, and thus email, was the medium between universities that we know of. Sendmail was included by default in each UNIX from that moment on; when you connected to the internet, you could already send emails.
The conditions were very different, it doesn't make a lot of sense to compare it to what we have today.