I think the edgier, more brutal, but yet, relatable characters came along like (the X-Men) and guys like Frank Miller with Batman who wrote this corny and campy character as a true Dark Knight with grit, agony and despair.
Once the early 90's folk started to transition into that type of anti-hero type thing, Superman was left in the balance as a kooky Boy Scout who got under peoples skin by being too powerful and too good to even care about once you had characters on the other side of the coin who had problems and had tendencies to use their weakness as a strength other than the other way around.
Once the Death of Superman arc followed by the instant Return and lousy writing, the character suffered through love stories like the Lois and Clark television show and writers giving him a voice that spoke in a cheesy way. There was no alternative and no depth to the character, just a hero in blue tights doing things as perfect as possible and stuck in a Chrisopher Reeve world.
The world was ready for something different and Singer's 2006 Superman Returns kind of was the last straw to the Supes character stuck in mud. By the time Returns came out, we had the evolution of Spider-Man, the X-Men movies and Batman Begins going into a whole new path.
Now, with TDK trilogy coming to a close, people are kind of opening themselves up to teammup, campier movies with action sprinkled in when Superman is making up ground to become edgier so-to-speak, which now, is basically becoming an oversatured market.
It's really hard to put a finger on. Superman for so long was treated as this outdated, pulp-cultural icon that the higher-ups refused to pay most attention to. If new things were tried, eventually, the character would fizzle right back into a Donner-verse setting and the same 'ole stories would be told weekly and monthly.
MOS is an effort that is trying to revolutionize the character into modern times, which I love. Problem is, the creator's over the last few decades neglected fresh starts and creative ways to push the character forward, but instead, kept going back to what seemed comfortable and that's what is STILL hurting the Superman character today.