You see, CBMs, as the name suggest, originated from comic books; and when writers wrote comic books, they have to make sure that the characters are not drastically changed/ transformed in each issue, so that there are something to write about next week. This led to the "monster/ villain of the week" style of writing that pertained for some time. More recently, there are storylines in comics instead of "monster/ villain of the week", which is an improvement; still, most often the characters are not drastically changed/ transformed by the end of the storyline, except in one-off series graphic novels such as Watchmen, V for Vendetta and Batman: The Killing Joke (shush, you know it is a one-off story when you read the last page, even though they adapted Barbara's crippling shot into the main DC timeline).
I have to bring this point up because I have read a lot of articles suggesting WB/ Disney/ Fox/ Sony use certain storylines from the comics as the story for a movie, and when I read the suggestions, often I find the suggested storylines have the flaw mentioned above: the characters, or more specifically, the hero (Batman/ Spiderman/ ...), are not transformed after the story. (Let's not mention One More Day.)
I am not saying that these storylines are rubbish, but the fact is that the storylines suggested do not serve the movie medium. One of the reasons I love Christopher Nolan's The Dark Knight Trilogy so much is that much focus were put onto developing the characters and giving them character arcs and transformations. For example, Batman Begins, Bruce Wayne went from rich kid to vigilante (most origin stories does that); The Dark Knight, Bruce Wayne went from respected crimefighter to hunted outlaw, his crush is dead, his ally is dead, heck, even James Gordon and Alfred got transformed in TDK and TDKR. Character development and journey is one of the main elements of what makes a good movie; if a studio were to use a storyline from the comics, they better change the story so that the hero have to go through some personal transformations; otherwise the movie would give a feeling of "not-a-great-loss-if-you-miss-the-move-somehow" in the grand scheme of things, seeing that most studios like to build big cinematic universes now.
And I am not saying the storylines from comics that I trashed so much above has no value, not at all. I think they could be great source material for comic book TV series, as the nature of comics serve the nature of Tv series better, need proof? How about the DCAU cartoons and Avengers: EMH?
What do you think? Please comment below!