Given that people were once given shock treatments and even lobotomized for being nudists, I think it's a safe bet that it's not TV.
Nudity on TV is usually sexual...but then most everything is, even when sexually repressive it's still got sexual undertones at least, because that's what draws viewers. In contrasts, nudists generally don't view nudity as erotic, and plenty of nudist colonies and such will make an effort to weed out those looking for a sexual thrill.
Interesting enough, in cultures where women typically wear full body clothing, even the sight of a woman's ankle will be intensely erotic and vulgar (one reason women might dare to wear ankle jewelry, to draw attention to her ankles) whereas in cultures where women go topless, breasts aren't seen as erotic and are completely casual. Of course people outside those cultures often don't understand that, because they believe the subjective reality they were raised in is an objective reality true of everyone.
Perhaps it's the allure of the forbidden fruit (people want what they can't have, and that seems doubly true of love and lust), or maybe just seeing something taboo excites the imagination, I don't know. But nudists seem to work from a different reality, though I'm sure there are erotic nudist camps and places as well.
And then there's the Victorian times. Porn and prostitution were generally heavily regulated if not prohibited (at least officially), but pix of naked children were surprisingly common, including of one's own children that were then hung up in the home for visitors to see. This didn't represent erotic titillation for them, but rather innocence. (Of course, people sharing naked pix of their children today will be called pervs while many of the things Victorians were harsh against--yes, I know it's exaggerated, but they were still harsh by today's standards--are now much more tolerated.)
Oh! Here's a bit on nudism in Germany (and how it shaped the hippie culture), it seems to be that it's about a quest for a return to innocence, and perhaps escaping the bonds of civilization:
http://www.hippy.com/modules.php?name=Ne...le&sid=243