For example we often see posts on HN about, "see, it's possible to write very fast software in language foo!" And most of the time yes, especially on modern hardware, most languages do allow you to write surprisingly fast software!
It's just that the people who actually want their software to run fast -- and who want it enough to prioritize it against other, competing values -- those people will generally reach for other languages.
With JavaScript, the primary "value" is convenience. The web as a platform is chosen because it is convenient, both for the developer and the user. So it stands to reason that the developer will also make other choices in the name of convenience.
Of course, there's weirdos like me who take pride in shipping games JS that are eight kilobytes :) But there are not very many people like that.