Someone else did it a different way

"Because we've always done it this way" is an absolutely horrible reason to continue doing things in the same way.

It's expensive to always do it the same way.

This should be obvious.  Unless there is a specific legal reason to do something in a certain way, the cost of it will never go down.  As a matter of fact, it will go up if there is nothing putting a cost pressure on it.  It won't improve AND it will cost more over time.

It's boring to always do it the same way.

Nothing is more menial than the exact same thing day after day.  People placed in this situation will burn out or become completely ineffectual.

It kills prioritization to effect change.

When the time comes to consider and evaluate new responses to problems, this one single phrase prevents action.

It supports continuing lack of awareness or understanding.

For every new technology and new way of doing something, there was someone that understood an awful lot about the previous technology or method.  Entire businesses rise and fall based on foundational improvements that cannot be achieved without knowledge of the topic.

It utterly halts innovation.

There's no reason to change something that works well is a corollary.  People learn by doing.  In doing, they make mistakes.  Most of the mistakes are not useful and they are costly.  But, some of those mistakes identify great new paths.  Those mistakes are part-n-parcel with improvement.

Someone will do it differently.

Then there will be that moment when you are left wondering why.  It's because someone else did it a different way.