Why do people think a small baby is so cute when he had to struggle for his life since preterm birth? Should give sympathy.

Eye of the beholder. Babies cause a lot of different reactions in people. None of these reactions are "good" or "bad". A preterm baby can be "cute" just as any baby. The same holds true for children with disabilities. Yes, some children have had to overcome obstacles, but that doesn't mean we should always pity them rather than delight in them.