Actually the brain is involved although that’s not much of an explanation as the brain is involved in everything you do. My thought is you are just a lazy ass but research tells us that when you procrastinate, your limbic system is overpowering your prefrontal cortex. It’s choosing immediate pleasure (like watching Dancing with the Stars) over the pain of a difficult task (like watching The Kardashians).
I’m going with “just lazy.” It’s Occam’s razor, the philosophical principle that, when faced with multiple explanations for the same thing, the simplest explanation is usually the best one.
Just do it. Quit your whining; that’s my department!