So what exactly is the problem with replies to posts where lots of text,
sometimes for 5 exchanges , is left on ?

is it a technical issue ..like it fills up storage capacity somewhere ?
( understandable )

or it is it just that it bothers some people that a lot is left on ?

I'll say what I sure do not appreciate..
is a response to something with no indication of what or to  whom the
person writing is responding to.
Like the post by itself if fairly useless that way.
Like say they write "I think so too." but you can't tell at all what
they are talking about unless you go digging.
I think that's just plan dumb.