Why do men AND women! Glance at my chest!?

I am 5'2", with a B cup. I have been told they look bigger than that by another woman. The point is that when I wear a shirt, that's not low cut, but not high either, just showing a little bit but not , just the skin above my , I get glances from the older men I work with, but also the women I work with will glance too! This always happens while we are talking! What are they thinking? Why are they looking? Don't they think it is obvious that I know they are doing this? And it's not like I wear low cut tops, so I'm just curious! I'm about to start wearing turtlenecks all the time!