I have a lot of theories. They’re all wild conjecture. :D But if you look at the writing credits for the various seasons, I think you can see where some of the problems may be happening.
Aaron Sorkin is an american writer/showrunner who is known for micromanaging, not listening to anyone else, and has his name on this many or more scripts. His shows suffer from the same lack of quality IMO.
I had an anon drop into my inbox to point out Aaron Sorkin also (I hope you don’t mind if I just answer you here anon :D); I hadn’t realized he also did this, but again I think there are cases where people can get away with doing things this way because they’re straight-up brilliant. Or, as you say, you can see the fault lines in the finished work where they probably should have done something different (but still managed it anyway because they know what they’re doing with a story).
The thing with Aaron Sorkin is, his writing is very distinctive. He’s another of those writers you recognize right off just by the way his characters talk and the rapid-fire pace he sets. (Joss Whedon’s dialogue is similarly very distinctive and I think for a lot of us even shaped in some ways our own language development, but the difference there is Joss found writers who could do that, too, to the style he set. Delegating!) Maybe he does a lot of his own writing because he’s not confident that anybody else can emulate that style, or maybe he’s just a control freak, whatever, but he can pull it off because he’s actually good. I’ve seen a few seasons of the West Wing, which I thought was great, and I was a HUGE Sports Night fan, and the fact that he did so much of it himself tells you that the guy’s talented. Like pretty much any show ever, problems crop up as the show goes on, and sometimes they’re big and sometimes they’re small… I thought Sports Night season 2 suffered when they started getting too much into the romance drama right away, but I will still slowly sink into the sea clutching that show to my bosom. As far as I can tell Sports Night was his first time writing episodic television (he has written by credit on 32 episodes out of 45) AND his first time as an executive producer (or producer of any kind). So you look at something like Sports Night, which is a comedy that still delivered on dramatic moments that if you bring them up right now, YEARS later, I will cry like a tiny child. The dialogue was snappy, the relationships were complex, there were terrific female characters… god there was that speech where Isaac absolutely fucking DISMANTLED Dan for comparing himself to Rosa Parks. Jesus that show was so fucking great. And THAT is why Aaron Sorkin can get away with it.
Several people have also mentioned J. Michael Straczynski, who produced Babylon 5 and as far as I can tell has writer credit about 100 episodes just of B5 and Crusade, not to mention B5 movies, and other movies, and all sorts of stuff. But as those folks have also mentioned, JMS was obsessive about pre-planning for things like actor exits, he had a very comprehensive show bible, he’d mapped out the storyline for like five years in advance… there are still places that you can see he was scrambling to meet the daily challenges of producing television and had to change direction in a hurry, but he also went in prepared to be flexible, and while we’re talking experience, the guy had already been working in television for a long time; he’d worked on some seriously popular projects like the 1980s Twilight Zone, Jake and the Fatman, Murder She Wrote, He-Man, She-Ra… shit, the guy literally wrote the book on screenwriting. :D
Like, I’m not expecting Jeff Davis to be producing something like Sports Night. I’m not trying to hold him to a crazy high standard. Teen Wolf is the type of show that I’d call a guilty pleasure if I ever felt guilty about my pleasures (totally don’t), and I’m not expecting the next great thing here. (I just came out for a good time and honestly I’m feeling so attacked by these plot holes right now.) But the guy’s not even trying. At all. And worse, it seems to stem from his belief that the audience doesn’t notice and doesn’t give a shit about things like Derek mysteriously having a sister who survived (ugh his whole thing is that THEY’RE ALL DEAD) and there’s never even a moment on screen where we even get to see him ask her, like, “how did you survive the fire?” Nevermind that she’s literally just a placeholder for another character who’s gone, which is bad enough, they don’t take the time to offer us an explanation. I’d even have taken a stupid, outlandish explanation.
I guess what it comes down to for me, and why I get so worked up and irritated about it, is that Jeff seems to be constantly saying, “Eh, the viewers aren’t paying attention, we can get away with it,” instead of saying, “The viewers aren’t paying attention… what are we doing wrong?”