Clothes are the same - look at any old pic from the 1950s of people in the street, and about 90% of people aren't dressing to look cool, they're just wearing clothes to suit whatever weather it is.
Design changed all that and it's the same with maternity clothes - celebrities like Myleene Klass are often seen in very stylish maternity outfits, and the months of pregnancy are no longer on a lesser fashion level.