Or is it that they are considering breasts as private now, when they weren't (or not as much) as before?
If it's normal and there's no social stigma, then who cares. But now if there is increasing stigma, at least in that the images could be used against you in the future, then that seems more like the problem.
This is probably in the article (I haven't read it...), but my guess is, in the past they probably didn't care if people had a glimpse, there were no cameras, and most people were polite enough not to ogle; but nowadays people can just pull out their phones and record for (presumably) their sexual gratification later.
Warning, this is analysis from not an anthropologist/sociologist: Maybe the prevalance of porn and screens to view them on has also made for creepier men/men who are now more used to viewing women as objects. I remember reading an article many years ago about how teenage girls are acting more like porn stars because they believe that's what attracts guys...
"but nowadays people can just pull out their phones and record for (presumably) their sexual gratification later."
As someone who grew up as a teen without a phone, I can say that mental pictures can be enjoyed (even without ogling), and it was very common.
I agree that the second paragraph is likely. Although if the girls are acting more like pornstars, wouldn't that make nudity less of an issue (or more normalized) even with a sexualizing audience?
If it's normal and there's no social stigma, then who cares. But now if there is increasing stigma, at least in that the images could be used against you in the future, then that seems more like the problem.