Why? ... because we've always done it that way!

Unashamedly nicked from Alec:

Monkey Experiment Proves Corporate Policy Process

Start with a cage containing five monkeys. Inside the cage, hang a
banana on a string and place a set of stairs under it. Before long, a
monkey will go to the stairs and start to climb towards the banana. As
soon as he touches the stairs, spray all of the other monkeys with
cold water. After a while, another monkey makes an attempt with the
same result, and all the other monkeys are sprayed with cold water.
Pretty soon the monkeys will try to prevent it.

Now, put away the cold water. Remove one monkey from the cage and
replace it with a new one. The new monkey sees the banana and wants to
climb the stairs. To his surprise and horror, all of the other monkeys
attack him. After another attempt and attack, he knows that if he
tries to climb the stairs, he will be assaulted.

Next, remove another of the original five monkeys and replace it with
a new one. The newcomer goes to the stairs and is attacked. The
previous newcomer takes part in the punishment with enthusiasm!
Likewise, replace a third original monkey with a new one, then a
fourth, then the fifth.

Every time the newest monkey takes to the stairs, he is attacked. Most
of the monkeys that are beating him have no idea why they were not
permitted to climb the stairs or why they are participating in the
beating of the newest monkey. After replacing all the original
monkeys, none of the remaining monkeys have ever been sprayed with
cold water. Nevertheless, no monkey ever again approaches the stairs
to try for the banana. Why not? Because as far as they know that's the
way it's always been done around here.

And that, my friends, is how a company policy begins.