Because it's not just an 'ignoring of errors', it's the fact all exceptions (as in actual errors from the runtime) are silently swallowed. In your example, if you typo in that function body, an exception will be thrown, your program will exit and you will see the stacktrace.

  var fs = require('fs');

  fs.writeFile('foo.data', function(err){
      // A typo here will lead to an exit and stacktrace
      sadsad
  });

Whereas in the Promise examples it is quite literally silently swallowing ALL exceptions thrown, including typos etc.

It is limited to Promises, because they're supposed to help us deal with error propagation, and pass exceptions through to `.catch()` handlers. But if that catch handler is missing, crickets, even for outright invalid code. That doesn't happen with any other construct in JS afaik.