[sfn42]

The problem is people don't adapt properly. If the business requirements change so much that it invalidates your previous work then you need to re-do the work. But in reality people just duct tape a bunch of workarounds together and you end up with a frankensystem that doesn't do anything right.

It is possible to build systems that can adapt to change, by decoupling and avoiding cross cutting concerns etc you can make a lot of big sweeping changes quite easily in a well designed system. It's just that most developers are bad at software development, they make a horrible mess and then they just keep making it worse while blaming deadlines and management etc.