Probably because AB doesn't want to have to listen to the sure to be endless blather from people who think it's OK and people who think it's awful to do so. And AB is correct in this.

because the "superstitions" should be the sub-category of religion. ..

Because religion is real and so is God and to put it there would be insulting to any person that follows a religious belief.

Because AB has to answer to their advertisers. Upon whom their revenue and their paycheques come from.

Because religions are not superstitions.

In order to avoid the type of answers you're getting right now. Also, AB tends not to double list categories unless they are completely different questions--like there are doubles for certain sub-cats because AB considers health questions and sexuality questions to be different, and divides things alone those lines. AB has set up a system where sexuality questions are with other sexuality questions and health questions are with other health questions, instead of mixing health and sexuality together and categorizing by body part. AB recognizing the two main types of questions likely to be asked and split categories accordingly and created duplicate sub-categories when necessary. What types of questions would be under this religion sub-category that wouldn't be under the other religion sub-category? Are you seriously advocating doubling a sub-cat because it isn't where your beliefs are? Or are you advocating moving it because it isn't where your beliefs are? It's an explosive enough section already, and you can find it easily enough. How about this, give solid reasoning why should it be under the sub-category of superstitions. Explain what you would do, double the cats, move them, and why they belong where you think they do over where they are now. Not just based on your beliefs, but on usability--what's the advantage for the site, in doubling or moving the cat? Make a good argument, don't just incite a riot.

grow a brain