Why do you think that is, generally speaking? Do they feel like large breasts garner unwanted attention, or is it something that isn’t even on the radar?
2.) What you said, where they don't want the unwanted attention. In the case of women who are over 40, a lot of them also lived most of their lives in a culture where a woman with large breasts was considered to be 'asking' to be sexualized. Books, TV, movies, etc. In addition, if they're from more conservative communities there's a focus on not 'tempting' men and the knowledge that if they're harassed their communities will just be like 'well you didn't hide that you have large breasts well enough, of course that happened.'
3.) A desire to be 'normal'. This group calms down when I mention that the current sizes that are carried in most stores were determined back in the 60s-70s and that their size is normal, the major American companies just like to coast on bad and outdated data. (Because why change if people still buy them?)
Since you often can't return a product that has been worn next to human skin perhaps the companies selling bras have realized that being able to sell more bras until a person figures out the right size is profit? Just one example of where obfuscating size/quantity/other_parameters is used for profit. For example, a "2x4" is actually 1+1/2 inches by 3+1/2 inches? This has been going on since the time of the Egyptians when you had to bring your own scale to the market to weigh goods, and watch out for the thumb on the scale.
