In a real life setting, it'd be more like Cast Away, where it's largely the environment that is the danger. Better to have some scrap of clothing to protect oneself rather than risk being naked all the time.
Of course, this being just Naruto hentai, I'm guessing it was Tsunade, Sakura, and Naruto's attempt to retain their dignity and be polite for one another. Being stranded and naked alone on a deserted island is one thing. Totally different level of uncomfortable when you have another person with you, especially if that is person is the opposite sex and someone you know.