wix-fetch not returning all headers

I am trying to get the headers from the http response when making a call with wix-fetch, however it does not return all the headers that are coming back in the request.
Here is my code:
fetch(‘http://www.instagram.com’, {method: ‘get’})
.then(response => {for (var key of response.headers.keys()) {
console.log(key);
}})

Here are the headers that it has:
cache-control
content-language
content-type
expires
pragma

However I use Fiddler to see the request/response as well and there are MANY more headers that are present on the response that are not coming through.

Can you provide any insight into why this appears to not work properly?