It's not that the authors are dumb. It's that humans are dumb, and that stupidity shines when it comes to anything creative, or rather, when it comes to the very complicated things that require an undeterminate amount of skills of various varieties - such as writing.
(after I wrote this, I went off the road into a weird rant)
Humans tend to place themselves at the center of their worlds. They'll do the most stupid and obvious mistakes in real life, where many before have made these mistakes - because they think they are infallible, that they are special, that everyone else is but a part of statistics, while they are something else.
Its hard to blame them. I believe that there is an objective reality independent of human thought, but nobody ever has been able to even glimpse at it. What we all see is the surface of the bubble that our mind is, and upon which the reality reflects.
We are realities upon ourselves.
Every person does something fascinating without even realising it, they create a world inside their heads. It's hard to put into words just how crazy I feel about this idea. It's insane, and the fact that we can do it inherently? Unconsciously? It scares me as much as it amazes me.
But that is also our shortcoming. A shortcoming as common for an individual as it is for a group.
We think that we are at the centre rof the world. That we are special. We create the world. We are the world. Except, we don't. We aren't. It's already there. We just make sense of it by incapsulating our experiences into personal bubbles that reflect a pathetically narrow and hopelessly incomplete image of what the world truly is.
So, when an author makes mistakes? Creates dumb scenarios? When the characters act dumb?
It's just an illustration of the shadows of the real world, left untouched by the surface of the bubble. Writing is a process that can be whatever you wish. No matter how much knowledge or experience you have, no matter how much time and effort and soul you put into writing, it will never be enough to completely exhaust the potential to what could be written, to what could be employed, used, applied into writing. No matter how far you stretch your bubble, it will never touch every part of THE reality.
Maybe those mistakes are precious in their own right. Ultimately, they, however little or much effort the author put into their story, are reflective of what it is that the author overlooked. What fell into the shadows of their bubble.
As much as they are a reminder of our inherent incapability and inconsequentiability, they are also a glimpse into what lies beyond us.