ide say its a combination of PS overkill + bad SNR + not a full reduction + Light pollution. When i take photos from down town perth towne
if i don't do Flats Darks and Bias the final image is shocking. the light pollution shows up vingetting badly. and hence you cannot push levels and curves.
Moral to the story, take flats darks and bias when taking photos in light polluted areas, other wise you will be pushing 5hi7 up hill on a flat bed wheel barrow!