tl;dr important to know the engine behind the languages

This might not be the reason for the author, but for me I understood Ruby limitation with ruby global interpreter lock. For smaller applications I knew this wouldnt be an issue, but when my applications began slowing down I would check the processes and understand that my Rails application are operating only on one single thread. Then I access if I should keep try optimizing or if something like Elixir is a better solution. Same process with JS