I don't know if this comment really helps but I think that its due to the particular nature of macintosh ux design where the red traffic is generally treated as command-w instead of command-q, so technically as the app is still open after doing a command-w its still within the same session which is why an empty app would simply start a new window/canvas/document if you click on the app icon in question because the user did leave it empty of any contents in a manner speaking
(even then I won't disagree with this feature request nevertheless as I can see it helping some users that don't actually close their apps)
