Well I’d say the thing is the debatable utility. CW delays a conversion, of course the utility of that is a lot more of a mystery that people can’t put their finger on, namely because nobody really knows how often it happens. in an unseen game n2-(day first unseen caught) if you assume your first barrier was not a succesful guess of the unseen’s target, barrier is all drawback no gain. As you could be preventing the assasain from hitting the drunk, or you could be making a non immune BD appear immune, or you could be making someone immune who is immune, but when they are called out on their immunity you think you need to vouch, because you possibly caused a misunderstanding.
The conversion immunity is the benefit and it is a damn strong benefit, the occ immunity is usually the drawback. because their are few non occupy immune classes that you can be semi-confident are actually BD.