[node.js] Why doesn't adding CORS headers to an OPTIONS route allow browsers to access my API?

Testing done with express + node + ionic running in differente ports.

Localhost:8100

Localhost:5000

// CORS (Cross-Origin Resource Sharing) headers to support Cross-site HTTP requests

app.all('*', function(req, res, next) {
       res.header("Access-Control-Allow-Origin", "*");
       res.header("Access-Control-Allow-Headers", "X-Requested-With");
       res.header('Access-Control-Allow-Headers', 'Content-Type');
       next();
});

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