It is not redirecting to your account, it redirects to the Google oAuth page. In order to be able to ask for the permissions needed to run reports and other features, MonsterInsights uses Google’s oAuth system. There is no difference between the whole page and part of the page redirecting to the oAuth window except that by using the whole page, as we do now, it makes it a lot easier for users with multiple Google accounts to be able to see it the right one, and it also eliminates the need for users to have to copy and paste the oAuth token code, something you have to do if you don’t use redirect.
If you had finished the flow, you would have been redirected back to your website.
If you don’t want to use oAuth you can also just use manual UA, located directly below the oAuth button.
-Chris