My opinion is that they are testing different ways to make players buy packs they otherwise might not purchase. It could work, especially since many in the community have severe cases of FOMO. While the dress looks great, I am not buying the expansion because I have no desire to play fairy occult sims. THe reason it may be locked behind that pack is because of the clothing style it may be clssified under, but I highly doubt many players even search by those tags.
I only purchased the Vampire pack for the victorian furniture. I have never played that occult. It was half priced before I even considered it. My teens purchased the Spellcaster pack and the Werewolve packs becasue it had gameplay they were interested in and we share my EA account.. Adding extra items to be pack exclusive isn't going to work on me, unless I was already planning to purchase a pack when it gets to a sale price that I can justify. The EPs with occults were normally purchased for the content that did not involve the occults.