This is a very complex passage, but in this case, women are "an excuse" because they are secondary to the clothing that is being designed for them to wear. The writer is trying to say that, before Chanel began to design clothing, it was "over the top" and far too complicated and decorative. In this passage, the writer is implying that clothing designers only had one goal: to make really flamboyant and detailed clothes. The clothing was SO complicated, though, that it became more important than the women who would wear it.