A big part of this is there is very little supply of people that know these languages well. Therefore, the good developers in those languages command a premium. Here I define “good developer” as those that have used it professionally or built significant projects with the language. I’d argue that, accordingly, PHP developers who use PHP7 and Composer can command a similar premium because a lot of PHP devs out there don’t know computer science fundamentals or how to structure a web application with modern package management and frameworks like Laravel.