If you think of a sporran as a handbag that is worn round the waist, it is easy to see where they are coming form as the purpose and reason for having them is the same, at least if the woman is wearing a skirt or dress. In the UK generally only 1 carry on is allowed and handbags count. Personally I have never been challenged on my sporran, but if need be could always slide it into my backpack/camera case. My wife always has to put her handbag in her backpack.

In the aircraft, I have been asked to remove a small bag from my waist because the seat belt went round it.