I’d qualify this to say approachable for the non-programmer.
Programmer have been happy doing what we do with C++ alone.
Which kind of goes exactly to the OPs question of How is something like COD4 done with scripting only?
Because tools dont matter; artists matter – engineers matter.
Tools are merely a way to get a vision that already exists in concept, to life. Your choice of engine is merely how you like your toolset, or appropriate to your pipeline.
As to why they continue to work that way? Because a lot of studios have large investments in not just architecture but also people.
Those people know how to use said internal software or processes better than if they hired new people with new skills and wrote or used new software.