How to cancel/delete Outlook.com from windows 10
 

I use gmail exclusively with two different accounts.

Every time I go to mail it always defaults to outlook which of course has no mail because I do not use it. Then have to go to another pane and then select which account I want to read.

I have not found any useful information on the microsoft or the outlook web sight.

I have right clicked on each account. The two gmail accounts offer the choice to delete. The outlook account does not!

Click on the Windows icon at the bottom left of your screen. Type in "Add or Remove Programs" then open at the top.

Click on Outlook when the window opens (should be on the right side of screen).

Then click on UNINSTALL program and follow instructions.

This is probably due to your usage of Cortana.
From Microsoft:
"Cortana requires you to sign into a Microsoft Account (MSA) in order to provide the best digital assistance experience. During the setup screens for Cortana, you are guided through the process of signing in with an existing MSA or creating a new MSA. The account you were using to sign into Windows 10 is referred to as a local account, and Cortana requires local account users to switch to an MSA as the primary login to their computer. "

So leave it installed or don't use Cortana.

Windows 10 users have one,but you don't have to use it. But keep the login and password just in case.

Instead change your default email:
Settings, Accounts, Email & app accounts, Add an account. Select Google, add account.
Now that you have your at\alternate email accounts setup you must tell Windows the default
Settings, System, Default Apps, Mail.