Fashion is hopelessly stuck on styles that existed 200 years ago. Baby doll smocks and faux empire looking fashions for teens were popular in the Empire era. Only then, pregnancy was to be expected and hence the looser waistlines. We were literally (at least over here) building a nation, citizen by citizen.
But the fashion is inappropriate for today. It sends a mixed message. Look pregnant but don't be pregnant. What is a kid to think?