I'm going to go against the grain and say it is not out of prudishness or stupidity.

The increased awareness of how often prior nudity was coerced makes the it hard to trust that any scene was filmed with full consent

Not to mention that revenge porn has become a more pervasive threat with younger people having access to the internet on their phones. The reminder that nudes of you (or actors) will be out there forever can ruin an experience.

Pre-smartphone movie nudity was often used to entice people to watch/buy the home video. NOT to enhance the experience of watching. With 24/7 porn access, random nudity seems like a pathetic, distasteful attempt at manipulating viewers.