The cares of the world cause many to reject the atonement.

An omnicompetent God leaves all mortals free to choose, but how grateful we should be that God chose long, long ago to rescue and to resurrect all His children through the Atonement of His Son. Nevertheless, some reject and many are indifferent to these and other divine beckonings, mostly because they are too caught up in the cares of the world. They are strangers to the Savior, who is far from the thoughts and intents of their hearts (see Mosiah 5:13).
Author/Source: How Choice a Seer! Elder Neal A. Maxwell