I have been pondering upon this question for a long time now and over time I've come up with many different explanations and/or excuses to justify why one (or I) procrastinate.
One of the primary reasons I used to attribute to procrastination was environment. It was easy to blame the circumstances to which you are in to the lack of productivity. For instance if the environment was too noisy it was easy to deduce that it was difficult to concentrate. Or if one was not feeling well, every excuse in the book could be used to "get some rest" aka slack off. Or if the chair didn't give sufficient back support, back strain would prevent me from getting things done.
So when I found myself cruising the environment, I'd eventually takes steps to change the environment. I got a new chair, found more peaceful surroundings and the like. The initial positivity was great and some productivity followed suit. However as time grew, there were more problems with the environment. I missed the noise, the chair was still uncomfortable, and the list grew.
Now it doesn't take a PHD to figure out that what was attributed as justification for procrastinations were actually just excuses. This was a big realisation. Time came to now learn not to make excuses and find ways to get on with it. And I did.
However procrastination is just like that relative you have that refuses to leave you be. Or that kid in school who stalked you. Or that thing you did that time you wished nobody to know of. You could run and hide and for a while everything's OK - but somehow they find a way to creep up on you again.
So here I find myself somewhat procrastinating again. Don't misunderstand, I get what I need to get done but why can't I do it first time I get it? I have the time and most of the resources so no excuse there. Perhaps I don't feel that the task is challenging enough to warrant my immediate attention. Or maybe the fear that the problem too complex. Or perhaps I'm just not interested.
Some would categorise this as just being plain lazy but I disagree. Laziness is the action (or lack thereof). There's surely something deeper here. I don't get it yet, but I intend to find out.