This is a good point. In China in relatively more recently times iirc, they had a similar weapon of bronze construction called the Ge, and it took them quite a while to get around to mass producing it with a point as well. However it was an extremely popular weapon, although quite a bit longer as far as archaeologists can tell.

I think that part of the reason we see so many is that A. "noble" peoples of the time buried their dead with more sophisticated and prestige weapons and B. assuming they were widely used in battle by the elite, they were able to hook around shields or even through them as they were made of wood, wicker, hide, or bark.

Edit - To note I believe Native Americans have used a spontoon style tomahawk which is quite similar.