Why is it customary to ask a pregnant lady how she's feeling?!

Kristyn • Married to a very entertaining guy! We have a puppy named Dolce and a baby due in jan
I don't understand America's need to ask pregnant women how they are "feeling". Because there are multiple scenarios of how she's feeling and none of which she'd probably like to discuss w just anyone. 
1) sick all the time and wants to punch the next person she has to explain her morning sickness to because she was doing ok until u brought it up again! 
2) feels fine - and acting normal - so y r u even asking me? Do I look bad? Or u tell them ur not sick and they tell u about every pregnant person they know that was/is sick... It's like they are telling u how abnormal it is that u are not sick ..
3) feels ok but digestion is wacky - constipated, diarrhea, gassy, - none of which she wants to discuss with you
4) tired. So tired. Which means this conversation is draining my sparse energy - 
5) crazy. I feel mad, sad, happy, excited, hyper, and sleepy all at the same time and have no idea how to explain it to u. Plus I don't want to tell u how crazy I am. 
And there are many more scenarios ... but no matter how she's feeling why can't people just say "you look great, congrats" just give me a compliment. No matter what, a nice compliment will make her feel good.