Lack of accountability
Accountability seems to directly affect productivity. When the task at hand does not have a hard deadline and there is no external pressure to do it, delaying the task becomes very easy. If doing it now vs doing it later has no real differences, then your mind will always pick the latter. And as they say, tomorrow never comes.
Creating accountability in these cases helps forcing your into actually doing the task. When you tell someone that you'll do something, shit becomes real. Now your reputation and credibility is at stake. You don't want to end up being a person who just promises things and does nothing. You want to be seen as a person who actually does what they decide. The level of accountability also matters.