Yeah I think there is just a lot of friction when moving from the concise "ES6" to the lengthy, and somewhat awkward "ECMAScript2015". The fact that so many people still use the terms ES6 and ES7 gives others even less incentive to use the official naming scheme. Hopefully, it will iron itself out in the future.
I think its not just the length but the concept: Every other language has a normal looking version (Rust 1.12 announced! Java 8, etc). They had that with ES3, ES5, ES6, then decided (perhaps for very good reasons) to change to a unique (?) version scheme.
