[rimunroe]

They decided on the "ECMAScript YYYY" naming format a while before the 2015 spec was finalized. Many people in the community continued to call things ES6 and ES7, but those aren't the official names.

[jsingleton]

I guess it's just a lot easier to type (and even say). For example, the current discussion on TypeScript: https://news.ycombinator.com/item?id=11920451

At least they didn't use 5 digit years. :)