I never thought about it in this way. How actors could possibly see right through a director or writers bullshit about needing a nude scene lol.I never considered them to be prudish, but when they read a script and theres no needed/necessary cause for their character to be nude in the scene other than "just because" then I can understand why they would opt or demand to change that scene. Nudity needs to be genuine other wise its just implemented for the sheer horniess factor of with the script writer, director or producer... and actors can see right through that.
On the other hand when it does make sense for a scene. An actor will sometimes use a body double or outright refuse. So even when it is truly genuine some still will have an issue.