I would argue that you can pick any new'ish (last 5 years) language that is suitable for development and find the same results. Anyone who knows the language w

I would argue that you can pick any new'ish (last 5 years) language that is suitable for development and find the same results. Anyone who knows the language well taught themselves how to use it without the guarantee of being able to use it at a job. This will be a fairly small subset of developers, the ones that have motivation and time to put into growing themselves. So this probably means that the devs that know new language X are just more interested in software development (compared to devs that just know the language(s) they learned in school, and whatever they were taught on their jobs). So they have a much higher chance of being good developers.