Comment by sjducb

The main reason why is to keep a handle on complexity.

When you’re in a project with a few million lines of code and 10 years of history it can get confusing.

Your data will have been handled by many different functions before it gets to you. If you do this with raw lists then the code gets very confusing. In one data structure customer name might be [4] and another structure might have it in [9]. Worse someone adds a new field in [5] then when two lists get concatenated name moves to [10] in downstream code which consumes the concatenated lists.