Why do people comment on how big/small you are if pregnant? Is it because they are trying to be nice or don't know what to say?

I never thought I would be annoyed by this, but people have been commenting to me lately how big I am in the form of: "wow you have gotten so big!" or "I wasn't as big as you" or "you must be due pretty soon!" I'm short and have a short torso so carry the baby very forward, so maybe that's why? (my midwife assures me I'm not any bigger than I need to be!) Also, I'm within totally normal ranges for weight gain (actually on the low end). I'm only 28 weeks and have a ways to go....and lots of growing to do yet!