It isn't just in the maternity unit that patients complain about hospital gowns. I remember reading a discussion among nurses once about how many patients complain about hospital gowns as being immodest and undignified, and what can be done. I think the general concensus was that people may be given two gowns for modesty, to be worn forward and backward. But the gowns are intentionally made generic with unattractive designs because if they were too nice people would steal them. Hospital gowns are intended to be functional and cheap, since they are often disposed of or lost.
I gave birth in a FSBS, and no one thought twice about what I was wearing or whether I was wearing anything. Mothers are encouraged to bring their own clothes. After dd was born, I found my abdominal area was so sore I could hardly pull the gown on that I had brought. They brought me a hospital gown since it is easier to put on. I thought it was wonderful and easy to nurse in, too. Obviously I changed before I left, but it served the purpose at the time until I felt more like getting up and moving.
Years later, I heard a birth center midwife answer a question a prospective client made regarding hospital gowns. She explained that the birth center does offer hospital gowns, but in the several years that she had worked there, she had never seen a mother use one. And I was sitting there thinking, "OK, I did use one there, does that make me really abnormal?" Oh well.