Hi Mujahid —
I normally answer comments much sooner than this, but for some reason did not receive (or see) the notification for your message. Apologies.
So, why not set more realistic deadlines? It seems like a simple answer, right? It’s not. A deadline is an artificial construct based on how we think the future will unfold. We can’t predict the future and cannot predict unforeseen events, blockers, hurdles, etc. There has been a lot of research around IT projects and the research consistently finds they are not delivered on time or not delivered at all. If you are familiar with the work of Daniel Kahneman and Amos Tversky, you might have come across the Planning Fallacy. It is a “phenomenon in which predictions about how much time will be needed to complete a future task display an optimism bias and underestimate the time needed.”
In short, we have a bias concerning how much time we will have in the future and how well things will go. Even when we add in buffer time, we usually do not make the mark. It’s just part of being human. Additionally, there are added business pressures where the release deadline is set by those who have no idea what the project will entail. And, you have other people who often steer the timeline as well.