>> Why does it have one?

To make sure that there's sufficient volume to provide balanced flotation for the designed hull length. Also to define the curves of the hull and deck panels.

If you make it pointy and keep it the same length, the stern will sink lower than the designed waterline and probably mess up the handling and speed. You'll also have a tough time getting the  stern closed.

If you really really have to have it pointy, leave the transom as is and build an extension onto it.

Laszlo

Thanks.

I thought that it might be there to make it easy to mount a rudder but I don't intend to put a rudder on this boat.  I was considering extending the sides but I like your idea of just adding on some materiel to the back of the transom and shaping as required to a nice rounded shape.