If I understand your question, you're asking why breast cancer is getting more common in younger women. I don't think anybody knows the answer.
One that was proposed that seems to make sense to me was, especially during the pandemic, there was greater consumption of alcohol. We know that alcohol is a carcinogen and is related to breast cancer risk as well as risks of other cancers.
For another example, we don't know why women are starting to menstruate younger. We know that lifetime exposure to estrogen is a risk factor for breast cancer, and women who start their periods younger and go through menopause later are at a higher risk for breast cancer. We've certainly seen that the age of onset of periods has become younger. It's not uncommon for girls as young as nine to get their periods now. It used to be that age 12 to 13 was the most common average.
I'm not an expert in this subject, but I've read that maybe it's because the girls who are young now, women my age, hopefully didn't smoke and drink during their pregnancy like our mothers did, and they're much better nourished. Maybe that's why they're starting their periods earlier, and maybe that's contributing to increasing rates of breast cancer.
There's a bunch of theories out there. At the end of the day, I don't think anybody really knows why it's happening.