Why might aboriginals have killed only the food that they needed?50-100 words

I agree with both of the posts above, and would like to add a couple of final points from a more practical perspective.

First, it would be difficult if not impossible in most situations for native peoples to keep and preserve large amounts of meat in that it was labor intensive to preserve it without the benefits of refrigeration/freezing, and the processes they used were not able to handle a large supply of meat at once.

Secondly, hunting by aboriginals in the days before both European contact and technology denied them of something else critical for hunting - guns and horses.  The Plains Indians for example numbered around 200,000 even after centuries of existence there, and a large reason for this was that they were not able to hunt and keep enough food to support a larger population than this.