In answering this question we need to bear in mind that Everyman is a religious allegory, which charts the life journey of the Christian believer as represented by Everyman himself. Despite his fundamental honesty, decency, and the strength of his religious belief, Everyman is a flawed individual, as we all are. Like most of us, he attaches too great an importance to the things of this world, failing to see that, though they may be useful to us on our life's journey, they won't lead us to salvation.
So although Discretion, Strength, Beauty, and Five-Wits help Everyman on his earthly pilgrimage, when it comes to the hour of his death, there's absolutely nothing more they can do for him. And so they abandon him. The next stage of Everyman's journey will be the passing over of his soul to the after-life, where it will be judged by God. What Everyman thought were his friends are no use to him now as they were purely related to the mortal world and all its vanities.