Again it's a preference thing... They do make a variety of different seats that could be used, several split seats, soft touch seats, etc all obviously at different additional costs.
but take the split seats for example some people love them, some people hate them, I have some seats that feel great in the hand if you hold in the right spot but if hold it any other way it feels awkward. Then you have the whole up locking/down locking thing.
You may find a set up you love, but doesn't mean every other person will like the same set up... Probabley why they just put pretty standard seat on most of the factory rods. Can't make the same rod with 6 different seats available...
that's why people get custom rods made I guess