Late Georgian (or in England, "Regency") fashion was much more risqué than fashion in the decades before or after it. It may be hard for us to realize this now, since we look at the womens' fashions of that time as much more "modest" than ours--though we would probably consider the men's tight pants much more risqué than ours.

Regency fashions are absolutely more revealing than fashions of the 1770s and 1780s. Women began to bare their upper arms during the evening, sometimes even during the day, which they had not done before--eighteenth century sleeves covered the arm down to the elbow. Necklines went lower; now cleavage was sometimes visible. Hoopskirts went away and women wore much narrower skirts with just a few petticoats -- or none at all -- or the skirts could be somewhat transparent -- or they might be dampened with water to cling onto the legs and lower torso. The limbs weren't "revealed" in the sense of wearing a miniskirt, but they were much more "present" than they had been before.

Of course this was "Grecian" or "classical", based on ancient statues--but if you see Greek statues you notice they don't have a problem with nudity, and that even clothed statues often have the body visible through the clothing.

Contemporary satirists pointed this out: The Fashions of the Day The Graces in a High Wind

Why did Regency clothes get so risqué? James Laver compares it to the 1920s -- in both cases, society went through an incredibly traumatic event (the French Revolution, World War I), and responded by getting a lot more party-happy and loose in behavior. In both decades, women wore clothes that were more like the children's clothes they had grown up in. There was dance mania. There was a sense that the living had narrowly avoided death and they were going to enjoy themselves as much as possible.

By the 1820s and 30s there was definitely a reaction against Regency fashion. Skirts returned to fullness, and even when they narrowed again in the 1870s and later they were never supposed to reveal the legs through the fabric. Thackeray famously refused to illustrate Vanity Fair--a satire about terrible Regency people--with Regency costumes, and dressed his characters in the 1840s style because he considered Regency dresses "hideous".

Not everyone, of course, thought the change was for the better. See this cartoon, where two young women in 1850s dress laugh at Regency costume. Of course the cartoonist points out that Regency dress is much more beautiful than their ridiculous flounces and huge crinolines! But the fashions of 30 or 40 years ago always seem ridiculous to us--think of our earlier opinions of 1970s and 1980s fashions. In fact, in James Laver's fashion timeline, 30 years out is when a fashion becomes "amusing".

We now think of Regency fashion as beautiful, and as more "natural", because we are far enough away from it. And it doesn't bother us if we wear 1920s fashion or 1970s fashion to a "decadent" costume party, because those eras are far enough away from us that their decadence is fun. (Isn't it interesting that we might go as "gangsters" and "molls" to a 1920s party? Very different than if we dressed as contemporary criminals.) But for Victorians who were trying to distance themselves from the Regency era and its immorality (perceived or otherwise), Regency decadence wasn't "fun".