GMail API SendAs GET not showing displayname without alias

Can't seem to find questions that address this directly but does anyone know why the endpoint https://developers.google.com/gmail/api/reference/rest/v1/users.settings.sendAs/list does not list the default displayName when an alias is NOT set up?

{
  "sendAs": [
    {
      "sendAsEmail": "foo@gmail.com",
      "displayName": "",
      "replyToAddress": "",
      "signature": "",
      "isPrimary": true,
      "isDefault": true
    }
  ]
}

From my testing, it looks like if you create an alternate display name using the steps listed here https://support.google.com/mail/answer/8158?hl=en, the response will show up as

{
  "sendAs": [
    {
      "sendAsEmail": "foo@gmail.com",
      "displayName": "New Alternate Name",
      "replyToAddress": "",
      "signature": "",
      "isPrimary": true,
      "isDefault": true
    }
  ]
}

And if you add another email address to alias, you get

{
  "sendAs": [
    {
      "sendAsEmail": "foo@gmail.com",
      "displayName": "New Alternate Name",
      "replyToAddress": "",
      "signature": "",
      "isPrimary": true,
      "isDefault": true
    },
    {
      "sendAsEmail": "foo2@gmail.com",
      "displayName": "Foo 2 Name",
      "replyToAddress": "",
      "signature": "",
      "treatAsAlias": true,
      "verificationStatus": "accepted",
      "isDefault": false
    }
  ]
}

But if you revert your main email's displayname to the original default, you get

{
  "sendAs": [
    {
      "sendAsEmail": "foo@gmail.com",
      "displayName": "",
      "replyToAddress": "",
      "signature": "",
      "isPrimary": true,
      "isDefault": true
    },
    {
      "sendAsEmail": "foo2@gmail.com",
      "displayName": "Foo 2 Name",
      "replyToAddress": "",
      "signature": "",
      "treatAsAlias": true,
      "verificationStatus": "accepted",
      "isDefault": false
    }
  ]
}

Was running into issues locally with Java but testing it on the "Try this API" features creates the same results so I am thinking this is WAD and I might need to be using something else.