A nice sentiment, but not reflected in reality. It's valuable to evangelise languages because
1. better awareness of their novel features can pressure more widely-used languages to adopt those features - like the addition of lambdas to Java, Python, etc.
2. otherwise you risk being stuck with whatever people know, forever. "Lack of fluency" is a technical demerit from the perspective of a project lead.Python has 76,979 job postings, Java has 72,743, and even lowly Perl has 14,802. Technical merit is not enough; those lesser languages need marketing.
The fact is, language adoption in the IT industry is very much a matter of luck, fad and fashion.
* whether the technology fits the background of your team/org/company
* the community/official support of the technology
* the long-term trajectory of the technology
* how the technology fares when used with groups of engineers, instead of individually
* social proof
* how easy it is for the existing job pool to learn the new technology
* if the technology has strong documentation
And there are more. These are more critical to me than eg goroutines. (And Go is my go-to language these days.)
But would _wldu have tried Go if he/she had never heard of it, and had no idea what features it had? Probably not; it's really hard to choose what you don't know exists.
Your own example demonstrates this. If none of your friends had ever mentioned Go to you, and no one had ever evangelised it, how would you have known that it's a good fit for that problem?
I hated Go when it first came out. I grew tired of hearing about it. My friends tried to get me to use it. I refused. One day, I needed to write some highly concurrent code, read about Go Routines, tried it and was hooked. I've been using it ever since. No amount of selling/proselytizing could convince me (nor should it). The language itself did when I took a serious look at it.