I was never a "princess girl" and I don't remember my sisters, female cousins or friends being princess obsessed either. It seems like more than 1/2 of modern little girls catch the princess bug which at least to my memory was not how it used to be. I and my cousins were much more into baby dolls (playing "mommy" etc) and barbies than princesses. Even with barbies, I didn't focus on them in a fashion-based way - I didn't change their shoes or brush their hair I just had them be teachers or doctors or mothers, etc.

I'm completely guessing but I think the rise in pricess stuff comes from the change in toys. If you go to target a huge portion of toys are pink, glittery and sparkly. When I was little slides, swings, etc mainly came in blue, yellow and/or red. Now everything from slides to swings to wagons comes in pink or blue, it seems like. So now if you buy the blue/yellow/red option it feels like the 'boy' one where in the past boys and girls just had the same slide and wagon that was the same color. It seems like from birth litlte girls have 80% of what they own in the color pink. When I was little a lot of clothes were pink but gender neutral toys were not pink like they are now, so maybe only 50% of my belongings were pink. I think kids learn to like what they are surrounded with. I have a nephew whos dad was really into football so when they were pregnant they made his nursery sports themed and by the time he was 2 he could shoot hoops in his little plastic basketball set and could hit a plastic ball off a plastic t-ball set. He was in multiple sports starting in kindergarten. He seems to genuinely like these things now at age 7 so I don't think it's harmful to him but I doubt he would have been as passionate about them if he weren't surrounded by sports from birth. If his parents were nerds and bought him everything dinosaur themed maybe he'd be super into dinosaurs. I think the princess stuff probably works out the same way.