Are you seriously suggesting that a password field in an online code editor on an HTML tutorial site is comparable to the situation we are discussing here?
Because it is insecure. Sure, that form doesn't actually do anything, but why not help and train visitors to expect security and know how to spot it?
w3schools is for web developers who are learning. Maybe they'll see that the page is marked Insecure and the lesson they'll get from it is that they need to secure their logins.