📝Some programming languages are popular because of the killer app/framework
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Some programming languages become popular when they bring a new killer app or handy framework. The popularity of such languages is tied to the popularity of the framework.
Example is Ruby and Ruby-on-rails.
For PHP, the first killer app was making HTML pages dynamic, now WordPress and Drupal.
C was basically the only high-level language for systems programming (other options were assembly and pascal).