Why did early modern humans event a spear thrower

The Cro-Magnon people increased their food supply by developing coordinated group hunting techniques for the killing of large herd animals, especially in the river valleys of Western Europe and the plains of Central and Eastern Europe.  They also developed new specialized hunting weapons.  The art of spear hunting was revolutionized by the invention of the spear thrower (or atlatl ) about 17,000-15,000 years ago.  This was a wood or bone rod with a hook on one end that fit into a socket at the base of a spear.  This device was used as an aid in throwing spears.  It increased the range and force of impact of projectiles by essentially increasing the length of the spear thrower's arm.  The net effect was that hunters did not need to get as close to prey before throwing their spears.  Toggle-head harpoons  were invented about this time as well.  The bow and arrow were invented by 12,000 years ago or a bit earlier.  This further increased the range of projectiles.  The fact that these weapon systems were developed toward the end of the last ice age is probably not a coincidence.  They were technological solutions for the growing difficulty of acquiring meat.