He isn't compatible with Current Year and doesn't fit with the narratives pushed in the clown world. He isn't 'outdated' so much as an actual hero in a world that currently wants Tony Stark's and Batmen. Damaged people who often leave the world as shitty as when they started out, or worse, but can say 'at least I tried' on their tombstone.
Very few people want to made the world a better place anymore. They are filled with bitterness and rage at previous generations, and they don't have the promised flying cars and moon apartments yet, so the ideals that Superman stands for don't mean much to these broken and disenfranchised people.
Hell, just look at the uptick in evil and fallen versions of the characters in recent years.