I have closed all viewports except one viewport and I maximized it. Next, I used SplitViewportHorizontal command. The result is shown in the following screenshot.
As you can see, both viewports are very narrow for no good reason. I tried to fill all empty space with these two viewports, but I failed. I could not extend the viewports all the way to the tabbed panels on the right side. I could not extend the bottom viewport all the way to the status bar either. The following screenshot shows the biggest viewports I could make.