The cut end provides a point for drawing your angled line up to a corner or an obstruction. Much the same as a drafting square (those triangular drawing tools) allow you to reach the point toward your final drawing destination.
I think the only answer, so far, is that there isn't a specific or vital woodworking reason.
Perhaps, a weak argument can be made that it allows the tang or blade to fit nicely into the stock. This agrees with the few references to this I've been able to find anywhere, including this one from the comments:
"The slot end is rounded whilst the other is ...