Just had a thought regarding why these aren't covered by the season pass. Technically these aren't "add-ons" to the game itself; they are merely avatars which you can use with your PSN account.
Therefore since they aren't directly involved with the game (although they are influenced by it), there is a price to pay for them. Of course it could have been a mistake as well; that's also within the realm of possibilities.
Was hoping that they would be covered by the pass, but at least the price isn't bad.