B S !
What skin color or race gets dominance in porn has nothing to do with the welfare of that race. So do you claim that in the 90s when white girls dominated porn it was because American Whites were poorer than Negros and Latinas???
The color and race is decided by the paying consumers, whatever the dominant demand is, that color will dominate the supply. So there must be a shift in the customers preference towards brown or light brown women, perhaps the generation of boys who watched Dora the Explorer has finally grown up?
After the color/race has been chosen by the customers, then yes the welfare of the different classes of girls may enter the play, e.g. within the white girls (esp. the blonde/Aryan end of the spectrum) group, there was (still is?) a period East European and Russian girls dominate the scene. But if they don't talk you can't tell their nationalities apart and otherwise you can't notice a difference in their performance from the more "classic" American or French or whatever nationalities porn girls came from, before 90s.