There was a terrible case awhile back in CA. A monster female had 5 kids-2 boys, 3 girls-and she adored the boys and hated her daughters. She hated them so much that she physically abused them, forced them into prostitution, and ultimately murdered 2 of the girls (forcing the boys to help dispose of the bodies in fires).
One of the girls who was later murdered escaped and went to the police. She told the police everything. And psycho mom shows up, explains the daughter is a pathological liar-and the girl was returned to her custody.
It is not at ALL unusual for kids to assume that no one will believe their word over an adult. So it's VERY possible Shawn calculated his chances of asking for help, being disbelieved, and being returned to a now-enraged captor who might make his captivity far, far worse , if he didn't outright kill him.
I believe the correct term for this thought process is "learned helplessness".
By the time kid is 5, he understand the concept of trust. By the time a kid is 11, sadly, he now knows the concept of mistrust and fear.
That boy was trying to stay alive.