@raiderrobert
There are many reasons for this.
Most of the time the assumption is that it's because the people doing the job are leisurely taking their time and/or fidgeting at something in the search of perfection, and the people doing the work will often buy into that assumption.
But most of the time it's because the organisation has introduced performance dampers into the project: progress meetings set to the calendar rather than milestones; resources being shelved and unavailable until after the point where they are needed; and that tendency for organisations to prioritise the urgent over the possible where the urgent is generally something that's been kicked into the long grass until the deadline frightened somebody high up. (In one organisation I worked for this last was called "phasing," and "We'll phase this project," meant you weren't allowed to do a damned thing until about a month before the deadline.)