Why Service Management? Why not just 'management'?
As Michael Hammer observed famously years ago, lots of things happen in organizations. Only some of them matter.
Services are special. Like the processes that Hammer talked about, they filter, clarify, and bring together the pieces required to deliver value. In fact, the very concept of a service involves definition of a specific value useful to a specific customer.
You can spend a lot of energy managing teams, projects, budgets, technology...you name it.
But, if you want to focus on value generation, services are a great place to start.