Atlas Quake

278px-Atlas_Quake_-_attacks-1-.jpg was Atlas so Unyeilding to Give up his Magic??
The reason why Atlas was not tempted to give up his magic to Kratos is because in the Ghoste of Sparta God of War Kratos is the one who inprisoned him under the earth after Kratos destroyed the pillar that once held up the earth when he killed Hades' wife, Persephone.

So Atlas was the new Pillar to Hold up the World.

Atlas Quake
When Kratos ripped Icarus's wings off he floated down to Atlas's realm in the Underwoald and traveled inside of the mighty Titan in search of a way to make it to the surface.

In his search Kratos found himself in the grasp of the angry god and was on the verge of being crushed before Kratos said, "I seek to destroy Zeus!" Atlas asked how he would succeed in this quest of vengence and Kratos replied, "By taking the Blade of Olympus back, and driving it into Zeus's heart! It holds the power I once weilded as the God of War!"

Then Atlas granted Kratos power to cause earthquakes and helped him across the great chasm that led to the Palace of the Fates.

I think that Atlas Quake is well used magic against large monsters such as cyclops' and ogre's and even Zeus. It is especially useful when it is in its last level and you are able to continually smash your fists into the ground.