It must have been bad for the furniture, but I suppose the hostess took her revenge on the furniture of her friends when, in turn, she visited them. Some of them were dressed fashionably, and they said they couldn't for the life of them see why you should be dowdy just because you had written a novel.

请教老师，why you should be...这里的should是“推定式”用法，不是表推测，也不是表义务应该。对吗？

另外，这里的推定式的should含有感情色彩吗？是“惊讶”感情色彩吗？怎么翻译呢？