Repression leads to lying.
It's human nature. Especially when you repress perfectly natural urges.
The more repressing a religion is, the more lying their members are. They are forced to lie.
Why so many priests and monks lie about their chastity/celibacy? Because they're repressed.
Why so many JWs lie about viewing pornography or masturbating? Because it's a 'taboo'; it's a repressed urge.
Excessive requirements lead to excessive lies.
Also, if you try desperately to build and maintain an image of a ''holy'' man of "faith" (as a 'good' JW does), of course you have to lie some times in order to keep that image intact. You can't make an omelette (image) without breaking some eggs (lying).