I'm not sure that I agree it has changed. To me, an allegory implies authorial intent. Some classic examples being Tolkien's friend Lewis whose Narnia novels were an allegory for Christianity, George Orwell's Animal Farm, an allegory for early Communist USSR, or The Crucible by Arthur Miller, an allegory for America's red scare.

If it isn't done with authorial intent, it's still absolutely possible to be a valid reading of the text that there are parallels, but IMO that's no longer an allegory.

[–] dragonfucker 5 points 2 days ago

The Matrix is a trans allegory, despite the fact that neither of the Wachowskis knew they were trans at that time. They put their feelings of gender confusion, dysphoria, and euphoria into the movie, despite not understanding those feelings. And it made it a masterpiece. That's proof allegory doesn't require intent.