It's basically recruiters saying "I want a candidate that can write a js app on the client,the html,the css, and can write all the server side code for it,manage the server,the deployment,the db, lead a team and do project management, all at the same time..." which of course is impossible.

Thankfully recruiting never is about what's possible... especially when it comes to the salary that should go with the "fullstack" requirement...

Now devs calling themself "fullstack" is another story...