Once a project has already blown its deadline, the activities added to wrangle the project back under control actually make the project even later.

Steve McConnell outlines some of these events in his book “Software Estimation: Demystifying the Black Art” - A few highlights:

More status meetings - because of the need to keep track of where the late project is, there are usually more status meetings. Instead of once a week, daily status check-ins take away from heads-down work.

More reestimation - looking for new target deadlines means reestimating at the expense of doing the actual work.

More apologies and discussions - the number of conversations outside of status meetings goes up, too. Rehashing the situation is common while getting a handle on the project.

More rework and technical debt - a missed deadline means cutting features (and often corners) to get the software out the door.

Managers fear that overestimating a project will lead to Parkinson’s Law - the project will take all of the time available. But the penalties which occur in an underestimation are much worse than when it is overestimated.