You asked me very early on why I didn't much care for comics today, and I think this may be the answer. Nobody is doing much imagining anymore. Think about it. How many new Batman villains have there been since, say, the early '70s? (Harley Quinn is the only one that comes to mind, and she wasn't even created by DC.) How many new characters has Marvel launched since the 1980s? How many new Spider-Man or Fantastic Four villains have we seen in that time? Where are the writers and artists who are willing to dive off the deep end, even within the established continuities, as I did with the darn duck? (And others did, too, with various other creations -- I wasn't a completely isolated phenomenon.)
With all due respect to the great Steve Gerber, this line of thought never has held water with me, because it implies that world building is a neverending process; and while innovation never should stop, there comes a point where the framework for creation stops being built, and you have to get to the phase where you start filling in the gaps. To strain the metaphor a bit more: after a while you stop building a house, the time comes to live in it.
This is not to say that some comics, unfortunately have been in a state of creative arrested development for some time, but that writers cannot be faulted if, after a certain point, you get a sense of what this particular series is about. In fact, I would argue that the clear definition of a Rogue's Gallery and Supporting Cast and worldbuilding are not a sign of absent innovation, but it's just a part of what happens to any type of good serial fiction at a certain point in their development.
MIGHTY THOR is an example of what I'm talking about. The original JOURNEY INTO MYSTERY issues gave Thor a new supporting cast member just about every issue; or a new villain from the Gray Gargoyle, Absorbing Man, and so forth. The orginal JIM is exciting because we see everything for the first time Some ideas have been a regular part of Thor's universe (e.g. the Enchantress, Bifrost, the Destroyer armor, Ego: the Living Planet, the High Evolutionary). All that has been established, and Stan and Jack did a great job. But there comes a point that, okay, now we know what Asgard is like and Thor can't just have a cousin of his or something pop up out of nowhere.
And eventually, niches start to form for villains. Let me go out on a limb here and say: does Superman REALLY need BOTH Brainiac AND Lex Luthor, for instance? The answer is yes, since Brainiac is different in many ways from Lex Luthor, however, the point is, in many ways they overlap, and this problem gets worse the more villains a hero gets. For instance, Walt Simonson when he wrote THOR, had to do gymnastics to show us why, in the story he was doing, the Enchantress's sister would make a better villain than the Enchantress herself.
More to the point, there comes a point where a writer can say, "why create a new guy, when Doctor Octopus would be PERFECT for this story?" And there is nothing wrong with that and here's why:
A villain, in their first appearance, nearly always, is only half an idea (with the exception of certain high-concept foes like Ultron, that were heavy-hitters from Day One). It takes later stories to establish who they are, exactly. In fact, villains only become a presence in the book the second time they pop up and a hero says "Oh, I thought you fell into your own destructatron last time!"
And after a certain point, villains become a legitimate part of the scenery of a book - they become supporting cast members, in a sense. That is, one reads DETECTIVE COMICS to see what the Joker and Penguin are up to as much as for Batman, and one reads AVENGERS for Ultron, Kang, Zemo and the rest. Using them is not an absence of the imagination; it can be, but often it is what the book is ABOUT.
Sticking to traditional villains is not a lack of innovation, but something inevitable (and, in fact, desirable) as comics get older, because the books get their own identity. This is not to say that infusions of new ideas aren't necessary, but there comes a time, creatively speaking, that you have to stop buying new toys and start playing with the old ones.
The most common complaint on any team book is that a character is "underused." Red Tornado is "underused." Black Widow is "underused." Even places, like Limbo or Kosmos have been called "underused." This is why many people resent the introduction of a character like Wolverine onto the Avengers: if you want a pragmatic, results oriented character with an espionage background in the Avengers...there are a half-dozen characters with history with the team that can be used instead of importing Wolver-freakin-ine.