Counterpoint has been happening since the motet.
Imitative counterpoint is when both the lines are using the same theme.
You state a theme, reiterate the theme in a second voice, and reiterate the theme in a third voice. Next you go off and do a bunch of other junk, and eventually end the piece. It also didn't help that when fugues were being written, there wasn't a fugal form. In the 1400's and 1500's people wrote fugues. Those pieces have been retroactively renamed ' canons '.