Until probably the last 5 or so years this was the norm. Until Node.js became widely used as a web developer you were essentially required to know JavaScript and at least one of Python, Ruby or PHP. For companies trying to shift away from these legacy environments or those who haven't started yet it's pretty reasonable for them to try and hire those kinds of devs still
Since people realised writing the same code in two different languages is a waste of time and the async-first nature of NodeJS/libuv is ideal for use in microservices.
Compare implementing back-end form validation in PHP and a completely different implementation front-end validation in JS vs using the exact same implementation on both sides. The former approach requires more work, creates a larger maintenance burden and a greater area for inconsistency and error because you need to maintain functional consistency between the two different implementations in the two different languages
