why are broad shoulders thought to be attractive even on women?

Are they? I have broad ass shoulder which make shirts sit weird on me. I think people generally find it more attractive in men

Who will protect me if I come face to face with a bear?

There seems to be an evolutionary preference for the body to have a certain basic shape. On men, that tends to be the shoulders wider than the waist and hips. The preferred shape on women appears to be one with wider hips, apparently. I think the idea that women with wide shoulders are attractive is a more modern, cultural preference. I assume it all has to do with fitness to bear and raise offspring, provide, protect and all of that stuff.

Not sure its the broad shoulders had a friend and his daughter was a college swimmer she was slender but her shoulders looked wider which made her body look tapered down to her waist

on women? i think not

It shows strength which we assume means you can handle problems easier

You can't change your natural skeletal structure. Whether a wide frame is attractive or not is just a matter of personal preference.