Those paintings were heavily influenced by classical art, in which nudity was standard. The classical nature of the subjects, and the classicizing idealism of of the forms and style, added a certain intellectual and aesthetic decorum to the works that seemed to remove them from mere prurience.
However, you must remember that these works were made for wealthy, educated patrons, usually for their private enjoyment and that of their like-minded friends. They weren't being displayed publicly, before audiences who were less educated, less sophisticated, and less likely to appreciate them. Nudity or partial nudity in religious paintings usually had some religious/historical justification (everyone understood that Christ wasn't crucified fully clothed), so complaints in that area were unlikely, though they sometimes did occur. Michelangelo's "Last Judgment" considered scandalous, and another artist was brought in to add draperies to some of the nude figures.
In other words, if a work was shown publicly, issues of modesty and chastity could arise.
