>>26977608
I guess that's the most probable answer, new warfare with a foreign nation. Though I should think it was actually good for what it was designed for given how proliferate it was in the region during the bronze age.
The only explanation I could find elsewhere is that it wasn't a practical shape to forge out of Iron and later materials.
I'd assume these are terrible for heavy stabbing, against anything better than light armor with a buckler, too. Maybe something to do with later armor development.
Eventually they were phased out to ceremonial purposes and symbols of power. Pic related, completely for show.