Do you mean on other discourse forums? Or other forum software? I haven’t seen it on other discourse forums.
But I think it’s done this way by design since most of the time people are reading and having the editor obstructs that view. Or when people want to reply to a specific comment, you’d click on the reply button there – which would already open the editor.
I think a better and easier way (as in already implemented) would be using the keyboard shortcuts to navigate the forum and reply (makes it so much better!). Here are a few:
j and k – Previous / Next comment (vim-like)
Shift+r Reply to topic
esc+r close reply box
You can also type ? for the full keyboard shortcuts.