Clause 126.96.36.199 is about contractors and the controls needed to control activities that impact your organization, the contractors’ workers and other interested parties in the workplace. Clause 188.8.131.52 is about outsourcing and ensuring that the arrangement and control for outsourcing are aligned with legal requirements and OH&S outcomes. The difference between these two may seem subtle, but if you look at the definition of contractor in clause 3.7 it becomes more clear; in the note for contractor it gives an example of construction activities.
So, the requirements are different because contractors are very often providing services in your facility (such as construction, electrical, plumbing, etc.) and as such the ability of the contractor to directly affect your workplace health & safety is much greater. You also need to worry about the health & safety rules that are being followed by your contractor employees when they ar e on your site.
By comparison outsourced services (such as computer services, accounting, etc.) can often be done away from your workplace and as such have less of an effect on your workplace health & safety. This means the controls for these services do not necessarily need to be as thorough. The standard separates these two types of externally provided services so that the requirements can be more clearly stated.