There's a lot more reasons that count for that. That became a very big social and political issue, which is a separate issue. I ask you then, how would we enforce this if non megacorps were forced to comply? Should decentralized media like Lemmy be forced to comply as well? Would US be forced to defederate with other country instances in the situation they may not govern their speech? Would encrypted communication that cannot be governed get banned so we can carefully make sure misinformation doesn't get spread? As soon as you think of the how would this be enforced, you quickly realize how terrible of an idea this is.

Of course it's easy to say misinformation bad, nobody is disagreeing with you. But actually going into actual practical solutions that maintain freedom and privacy is the hard part.