I always assumed a large part of it was escapism and rooted in fairy tales. Historically women and girls don’t have a lot of power, so this offers a realm in which they can have more power or one in which power isn’t a systemic concern.

I also think it allows for more fantastical conflict resolutions and a degree of separation. You can’t accidentally melt a witch with water in real life and the imagery is less concerning than a bloody and violent death.

I think most kids also know, consciously or not, that a portal to another world won’t exist. At the very least it’s unlikely, so there’s no real world witches or bandersnatch to worry about.

I don’t think this is all necessarily intentional, but I think it’s something psychologically ingrained in our patriarchal society.