Why do babies cry so much in plane ?

As I was traveling back from India, I was assigned an aisle basinate seat in British Airways. These seats are idle for moms carrying babies since there is a place infront of the seats where on can put the cart of the baby. But for me it was difficult. There was a lady who was carrying a few months old baby and was sitting next to me. The baby would cry intermittendly. I was feeling helpless seeing the mother who would try to pacify her by all means. I was happy to help her by getting the stuffs from overhead cabin, moving stuffs around etc. Holding the baby in her arms on her lap, she would reach out to her bag, take out milk powder and prepare baby milk while the baby was crying. I don't know how babies can express their pain, discomfort, probably by crying. May be the babies communicate by crying, as I could hear some other babies started crying at other corner of the plane . I don't understand how such young babies get strength to scream and cry at such shrill pitch. But as the mother fed the milk bottle in the baby's mouth, she gradually stopped crying. I was wondering the difficulties that mothers face to go through these situations -- she needed help, she was embarrassed and she was also in pain seeing her baby in discomfort. I was wondering what was going on in the mind of the baby. After feeding milk, the mother put her to sleep. Then she had her own meal. Then she put the baby in the cart. After sleeping for several hours, the baby was awake and then she was playful. I was observing the pinkish small toes and fingers of the baby. I was looking at the small watery eyes, her small lips which were soaked with milk and her tongue. It was so innocent to see how the baby would throw her limbs in the air. I was wondering how that baby would grow up to a full-grown woman some day.