If you open TextEdit and then click on the red x in the top bar of the document, TextEdit will remain open. This is evidenced by the little black dot under TextEdit, despite no TextEdit documents being open. Why Apple designed it like this? I haven't the slightest idea.
I've found a piece of third-party software that offers this functionality called "RedQuits."
Is it possible for TextEdit to automatically quit itself when the x is pressed, without installing additional software?