How to clipboard copy emacs help text by user-made interactive function kill-ring-save

[Budi]

I tried to clipboard copy some emacs read-only text by user-made
interactive function kill-ring-save, but fail
It's not M-w bound to kill-ring-save emacs built in function which is working

but as my preceding question, the copy :

(defun copy (b e)
  (interactive "r")
  (if (use-region-p) (call-interactively 'kill-ring-save)
  (save-excursion
  (beginning-of-line)
  (set-mark (line-end-position))
  (kill-ring-save (point)(mark))
  ))))
(global-set-key (kbd "C-c") 'copy)

cannot copy such case above,
any idea what's actually made different behavior of kill-ring-save ?