Wow, now we're complaining about the outdated versions of a language? Come on man. Nobody is going to write a modern application in ES5 and there are plenty of warts in old Java, C and Python applications as well. That's the nature of them being "old".

Why does that impact whether or not it's a reasonable choice to use the language today? Old libraries I could understand, but old independent projects? How do they affect the current state of the language?

Isn't it obvious? You apply for a job, company that isn't a startup has code that is likely written with old JavaScript whose replacement is not economical, so even if you do everything new in ES7, you still have to wade through old ugly code, likely everyday.