Because “men get too aroused looking at their nipples”
Masturbation is classified as a sin under Islamic law, which Indonesia has incorporated into its legal system. Technically, Indonesian law outlaws any “immoral behavior”, which this action would fall under. Sources indicate that while the punishment of decapitation may have once been enforced (in theory, they would have had to catch you masturbating, so maybe…
Reported here, Canada’s Supreme Court has legalized oral sex with pets as long as no penetration is involved.