As a term Digital Workplace was coined in a time when, to some, Digital Transformation simply meant 'going paperless'. The assertion here is that a Digital Workplace must be so much more and represent every corner of a business as a modern application that adheres to modern UX standards from consumer applications, often starting with the actual application being hosted in the cloud.
A Digital Workplace is often measured by how much of an "experience" working with it is for the employee. This is contrast to the more orthodox way where an organization has a laundry list of features that need to be supported by a business process, but how these tasks get done is not relevant to the application owner. Since this creates a lot of mundane or repetitive shuffling of windows, copy-and-pasting of content between tabs, etc., the 'Digital Workplace' was incepted as a vehicle to communicate that the how we work is as important as the task at hand itself.