Among the Jehovah's Witnesses, why are doubt, questioning, and dissent punishable offenses? Sometimes the offense will lead to be shunning.?

That's a major hallmark of a cult. Unquestioning loyalty to human leaders, punishment if you don't obey. The JWs consider that to question the governing body is questioning God Himself. It's so sad that people could be deluded and indoctrinated enough to believe that nonsense. They put no stock in what the Holy Spirit does by Himself, with no need of the governing body to help.

Because the WBTS is considered to be directly inspired by God by JWs. Therefore to question them about anything is tantamount to questioning God himself. The difference though is that we have numerous examples of even prophets questioning The Almighty without repercussion. In contrast, the WBTS will kick you out of their club quicker than you can say the word "shun" if you dare question them.

That is a characteristic of cults.