The "KISS" principle ("Keep It Simple, Stupid" or some gentler variation on that) has long been a key principle for effective living and business. It is closely related to keeping things affordable, as simplicity tends to be a good countermeasure against unnecessary expenditures.
In large-scale IT, keeping to these two principles is essential to maintaining the proper cost-benefits balance that keeps IT viable rather than it becoming an upward spiral of price and complexity.
So, this value of the "why" dimension is all about the business benefit of well-run IT. Over the years, many efforts have been made to document and codify how this is done - one of the more successful ones is ITIL - the Information Technology Infrastructure Library. Interestingly, this definitive set of guides that characterize a well-run environment is essentially the depiction of a functioning mainframe environment - in this case, the one at the British Government.
Where the software relevance comes in here is the selection of tools which create a layer of business-enabling simplicity, keeping IT easily manageable and consequently paying for itself. And that's an important business value!