Because it helps people understand why they do what they do and thus gives them a tool to not be a slave to their inner mechanisms, especially those that are harmful to oneself and others.
Because essential things are those that provide real joy and inner peace. Unessential things are evanescent and only offer momentary pleasure and gratification.
Because it is the only real thing that exists. The past is memory, the futur, imagination. Both exist only as thoughts in the head. Only the now is real.
Because only then will one find genuine joy and satisfaction and because those activities are thus done only for their own sake and not for the hypothetical gain they might bring.
Because that is what we are and that is the only way in which we'll be able to have meaningful relationships that are not sabotaged by our psychological mechanisms, by the image we want or fear to project, by our ego that is grasping at things or afraid of them.