I don't know, they didn't benchmark it and I don't have the config to try it myself.
My gut feeling is that it's possible the thread scheduling was tweaked so that the UI is more responsive for the Workstation variant, since there's generally a user sitting in front of it who might be doing something else while some video renders or code compile. Server, on the other hand, cares less for that and if a process really wants to max out CPU (like a build or a rendering job) it should be allowed to do that since there likely won't be any sudden UI users on the machine.
My gut feeling is that it's possible the thread scheduling was tweaked so that the UI is more responsive for the Workstation variant, since there's generally a user sitting in front of it who might be doing something else while some video renders or code compile. Server, on the other hand, cares less for that and if a process really wants to max out CPU (like a build or a rendering job) it should be allowed to do that since there likely won't be any sudden UI users on the machine.