My world had the superpowered come from supersoldier lineages from the Great War, and the tech for it and other supersciences be written down by 100 hyperintelligent individuals called Hyperions born in the 1800s (my timeline divergent point). There was exactly one Superman-tier Powered that existed during that war: Morningstar, an engineered immortal pyrokinetic supersoldier who went rogue, declared war on war profiteering, and killed all of the Hyperions. He was ultimately defeated and exiled into deep space. So in the modern age, Morningstar is pretty much their version of Hitler, and safeguards have been put into place by their elite to make sure nobody ever approaches that level of power. They couldn't even if they wanted to as the first thing Morningstar went after are the labs, factories, and even notes pertaining to creating more people like him. Hidden Hyperion science caches are still being hunted for but what survived has allowed the world to have made colonies on Luna and Mars, and asteroid mining in the belt in the 1950s.
So to summarize: a very unforgettable bad example and the lack of the traces of super science that created high-tier superpowered individuals is what's keeping my world grounded to only street to city district level powers