They have been trained to lie as a way of making their religion seem less extreme and more moderate. Their trainers have deceived them into thinking that such lying doesn't count as lying but is just the art of being tactful and not giving others the "wrong impression" about JWs.
Their trainers have given them the green light to lie by defining lying as
"withholding truthful information from those who are entitled to it.".
Their very definition of lying is itself a lie designed to justify lying! So JWs will lie to your very face without a twinge of guilt if they tell themselves that you're not entitled to know the ugly truth about some of their controversial practices and teachings like shunning persons who disassociate from the religion.