The folks at Google decided that when there is only 1 tab open, if you close that tab, the entire window or browser will close. This is obviously not what the user intends or expects to happen when they close a tab, even if there's only 1 tab open. When a user clicks the "close tab" button, they just wanted that tab to close (and there would be a blank new tab page). If they wanted to close the entire window or browser, they would click the X button in the top-right corner. Google isn't respecting Windows' UI. Unfortunately, Google has dismissed users on this issue without an adequate explanation. Please right this wrong in the Chromium based Edge! (I also just noticed that there are a lot of people in the Feedback Hub requesting this too. This has been annoying users for a long time!). I think you would be surprised by how positively people would respond to this change (assuming yous do fix this...)
Chrome, Firefox, and IE all close the browser when you close the last tab. I want Edge to do the same thing. If a change is made to the current handling of closing the last tab, it should be a configurable setting so that those of us who want to have the browser close when the last tab is closed can continue to have that experience.