Because if you are not in the present moment, you are either living in the past or future. That is ok if you are projecting good memories or positive hopes.

However in general when we are in the past or future, we are thinking about past traumas or fears/worries of the future.

When we are in those thoughts, our bodies produce hormones to reinforce the feelings that match our thoughts. (how you feel sad, upset, scared or angry) That's when our bodies are put to stress. When we do not know when to turn off those thoughts and feelings, then the stress becomes chronic....Chronic stress takes your body out of homeostasis...

Meditation gives your mind and body a break and a sense of control so you can navigate your mind and body to the direction you want to head...