The DC Multiverse is filled with worlds that can be radically different from the main DC Universe because of the slightest changes. One such change not only altered the general populace's perception of metahumans but also deprived the world of Superman. The change in history? A single nail gave Jonathan and Martha Kent a flat tire, thus preventing them from finding their would-be adoptive son. The resulting changes in JLA: The Nail (by Alan Davis, Mark Farmer) from not having Superman in the world led to a significantly different universe, even if its other defenders were still a part of the timeline.
Jonathan and Martha were delayed from their trip on what should've been a fateful day by a flat tire caused by a stray nail. It's incredible to think that such a small occurrence could alter the course of history, but that's what happened. As a result, they decided not to go driving that night. This meant they never found baby Kal-El when he crashed landed in a field. The ramifications of which were felt decades later.
Superman paved the way for all the other heroes that would make themselves known, setting an example for all of the post-war heroes that followed him. His courage, kindness, and hope were an inspiration for an entire planet. Even though he had godlike powers and could probably destroy the world singlehandedly if he put his mind to it, his genuine goodness helped the world accept him and by extension other metahumans that he associated with.
Without him, the metahumans of this world became reviled by the public and aliens even more so. Lex Luthor managed to achieve a position of leadership within Metropolis by creating a robotic police force to protect the city. The Justice League of America, even though it existed, was on the outs due to infighting and public opinion turning against them. To top it all off, a conspiracy was brewing against the metahumans and aliens of the world, all of it tying back to the missing Kal-El.
In this world, Luthor found the alien spaceship, but not the baby. All he found inside was a trace amount of DNA that he tried to graft onto human beings, intending to make himself a god. But these experiments all failed except for one: Jimmy Olsen. Now imbued with Kryptonian power and knowledge, Jimmy started a conspiracy to turn the Earth against its heroes and then remake Krypton enslaving humanity. The only thing that could stop him was the true Kal-El, who had been raised by Amish parents this whole time, which explained why he never showed up until the fight came to his doorstep.
So many changes were a result of this one event. It all circled back to how one man could make such a difference in the lives of billions. Without Superman, metahumans and aliens might not have been able to coexist with the human population without someone to extend that olive branch. Fortunately, this world's Superman was only delayed and not taken from them.