(or "Why? Because Bob Kanigher, That's Why!")
And a tip of the hat to Chris Sims for the subtitle...
Reading Silver Age Wonder Woman stories is, at times, like reading someone's dream diary. Flying saucer men animate parade balloons and send them on a rampage to conquer Earth, outer-space dinosaurs ride cosmic jet-streams from their home on Titan, an Amazonian "absolute zero" chamber freezes metal insects from space until they shrink down to nothing...every story seems to follow a surreal logic all its own. It's a completely different type of storytelling than we see in modern comics (for the most part.) And yet, this was common practice during the Silver Age. What changed?
A lot of things, obviously. The target audience got older, the writers became more invested emotionally in their stories, the editors became more interested in universe-building, and a dozen other reasons, but one reason that jumps to the top of the list is simply this: Silver Age writers had to write their entire story in one issue. These "one-and-done" stories didn't have a whole lot of exposition because the plot didn't leave room for them. In a modern comic, "flying saucer aliens" would be given six to ten issues of backstory, motivation, and initial appearances to lead into their attempt to conquer the Earth--back then, the writer just put in a little caption box mentioning that they were evil aliens, and the reader went with it.
Obviously, this means that the whole question of "decompressed" vs. "compressed" storytelling isn't easy to answer; on the one hand, much of the "decompression" of modern comics tends to be about extending sequences in order to heighten tension, instead of actually telling more complex stories (the death of Superman, for example, featured a whole issue of splash pages of Superman and Doomsday hitting each other. It heightened the intensity of the scene, but the whole fight could have been told in six pages.) On the other hand, compressed storylines frequently work better when dealing with children's fiction, because children are more used to the idea of a story having rules that don't necessarily make sense, but that are given to them by the storyteller and they just accept it. Pacing vs. padding, excitement vs. epic, it's really a debate with no end. (Save, of course, that a bad writer can do neither, while a good writer can do both.)
But we are, lest anyone forget, looking at "compression" vs. "decompression" through the lens of the storytelling engine, and the key question is always, "Does it help the writer come up with stories, or does it hurt them?" And from that point of view, compressed stories are a hindrance to a writer, not a help, simply because when you write a complete compressed story every month, you have to come up with six times as many stories as someone writing a six-issue arc "for the trade." As a result, Silver Age writers recycled stories a lot more than they could possibly do now, both by reusing story ideas (Superman was notorious for reusing certain stories every two years, in the firm belief that nobody who'd read it the last time was still reading comics), an by outright reprinting old stories. (Flip through the table of contents in an 'Essentials' and you'll see "Issue #XX reprints issue #YY" quite a bit. The phenomenon even had a name, "The Dreaded Deadline Doom." Seeing that when you opened a comic back then was like seeing "The Blue Screen of Death" for a computer user.)
Which isn't to say that modern writers don't reuse ideas (Brad Meltzer, I'm looking at you...) But they generally do so for different reasons. The climate of comics has changed, so that between decompression, willingness to sacrifice deadlines, and advance planning, nobody needs to whip up emergency stories. Compression forced Bob Kanigher to write quickly on 'Wonder Woman', and while that resulted in some of the most creative stories in comics, it also resulted in comics that made very little sense. Nowadays, writers don't have that excuse.