Damien

Also it's not as if it's only Doctor Who which does this. I think people notice it more in the recent Doctor Who episodes but messages within storytelling have always existed. People use the art of a certain time as a way to explore the period.

I think it's easier to spot it in scientific fiction because the created world makes it's more obvious when the writer has made an intentional choice of what to include in it. If they've created a society which has a class system for example it's clear the writer did that intentionally rather than it being a mere accident of the location it's set. It also gives the writer more scope to explore whatever issue they want since they're less limited.