Why is project scope management so challenging in it projects?

Project scope management are challenging in the IT projects are as follows:

As, the most of the projects are associated with the IT and the scope are basically used to ensure that the projects meet their expected requirement and should deliver on time. So, as a result if there is change in the project may also affect it financially.

Basically, in the software project time is money, the longer you spend time on project then more you loose money. Sometimes, the software projects requirement become too expensive to the organization to purchase then, it become more challenging to the project scope management.