It is not the nudity itself that is controversial. It is, like
@lolander mentions, the fact that there is always an allusion to something sexual and perverse.
Michelangelo's
David is nude, but he is not sexualised, nor does he hint at something sexual.
Derek Javis'
Gardeners Frolicking has the viewer watching them pruning, a mundane task, naked from the waist down, grinning as if to imply a sexual act.
If we are talking about controversial nudes, then do remember Édouard Manet's
Olympia, who was not controversial for her nudity, but for her confrontational staring at the gazer and the implication of her being a prostitute, which invites the gazer in an uncomfortable suggestion of a sexual act.
Eroticism can be fine / high art. Derek Jarvis' erotic paintings aren't.