i think people dont hide threads because seeing that squished greyed out, hidden thread bar on the board bothers them. if a hidden board fully vanished from their view, perhaps toggled on and off somewhere else, people would use it more instead of complaining.
Ive noticed from using other boards, as well as working as a mod on another chan - which i will not mention - users feel insecure and frustrated hiding posts because they dont like to be reminded that they had to hide a post, and having something on the board that basically says "hey this is the thread you hid because youre too much of a pussy to look at a PENIS" makes them not want to use the feature, and complain about the content instead, so the content doesnt appear at all.

its stupid, but having talked to many complainers over my time on IBs this tends to be the ''logic''. （ ´_ゝ`） its really stupid, but people are like that.