Still confused why docker works when you make a process listen to 0.0.0.0 but not 127.0.0.1

const hostname = '0.0.0.0'; // << This is where I'm confused
const port = 3000;

const server = http.createServer((req, res) => {
  res.statusCode = 200;
  res.setHeader('Content-Type', 'text/plain');
  res.end('Hello World');
});

server.listen(port, hostname, () => {
  console.log(`Server running at http://${hostname}:${port}/`);
});

When I dockerize this app and run it in a container, hostname 0.0.0.0 works, but 127.0.0.1 doesn't work. I understand the reason why is because docker containers pretty much get their own IP.

So when I build and run the container when I set the hostname variable to 127.0.0.1, and then visit 127.0.0.1 on my browser, I'm not connecting to the container's IP address, but my local machine.

But why is it when I run the containerized app on 0.0.0.0 and visit 127.0.0.1 on my browser, it now connects to the container instead of my local machine?

Thank you.