I think the fondness for first person (often unreliable) or third person limited viewpoint comes from a fundamental aspect of modernist philosophy. That aspect is that in modernist thought there is NO absolute truth. There’s my truth and your truth and (heaven help us) Kamala Harris’s truth. The Omniscient narrator belies this point, for that story, their narrative is the truth. They deny that such can exist in support of their raging relativism. I think the second issue is the types of “stories” they write. Plot is limited or irrelevant, the characters aren’t characters but more archetypes or mouthpieces for their viewpoints. They view the whole purpose of literature to essentially be propaganda. The more traditional is that we are telling a story. There is probably meaning there but in general rarely is allegory the prime purpose. Not to say this doesn’t happen, e.g. Starship Troopers is a polemic on Duty, but honestly, it is also a hell of a good story. Thirdly, the modern literature folks are oddly like what the Puritans were alleged to be. They’re afraid someone might be having fun somewhere and they must prevent that at all costs.