Neither do the people who designed Discourse, apparently.
But the issue is that in a discussion, it can’t be assumed that a reply will always reference the one just before it. As @GreysonCarlisle said, there can be misunderstandings. Even if you don’t quote, if you hit the “reply” button it will also remove the indication of who you are replying to.
It can also be useful to include the quote if you want to talk about the wording of the post, rather than making people go back to re-read the preceding post. Or to emphasize what a person said.
Regardless, it is silly that something like this is literally changing your post for no good reason. It’s the forum software equivalent of Dan Quayle correcting the spelling of “potato”.
However, for my purposes, I didn’t like that every quote would have five visible characters at the end in the editor.
And if I put the no breaking space in directly into the editor, it would be removed.
BTW, I believe you can also use ­, which is one fewer letter.
And this can be exploited, too. Use a whole thread reply to reply to the person above you, and they won’t get a notification. You could, say, challenge them to prove you wrong, and then they don’t because they don’t know you replied to them.
I do not understand why they wouldn’t at least leave the posters name in the top right, if nothing else.