It's because if you explain what's going on, you stop the action. And viewers/readers don't like that.
In fiction it's called an info dump. As an aspiring science fiction author, virtually every beta reader I've had has told me they don't like them. I want my fiction to make sense, but you have to be subtle about it. To avoid readers complaining, you have to figure out how to explain things to the reader without it being obvious that you're explaining things to the reader, or stopping the action to do it.
Movies are such a streamlined medium that usually this gets cut entirely. At least in books you can have appendices and such for readers who care.
In fiction it's called an info dump. As an aspiring science fiction author, virtually every beta reader I've had has told me they don't like them. I want my fiction to make sense, but you have to be subtle about it. To avoid readers complaining, you have to figure out how to explain things to the reader without it being obvious that you're explaining things to the reader, or stopping the action to do it.
Movies are such a streamlined medium that usually this gets cut entirely. At least in books you can have appendices and such for readers who care.