Right now, hitching posts work like vehicles, requiring a certain amount of Body Strength for an animal to be hitched. For a hitching post, this is roughly 15 Body Strength, based on the hitching post's weight.
Unfortunately, this means many domestic/common animals cannot be tied to them, including:
Hens / Roosters / Chicks
(For the sake of brevity I've only listed domestic animals; there are other tameable creatures that also cannot be hitched.)
I was really hoping I could use hitching posts for some of these, especially hens and pigs, since the trough would help out a lot, and the post itself helps position the animals to avoid overcrowding without having to use tons of fence posts.
So, why not just disable the Body Strength check, either for domestic animals only or for all animals?
The gameplay argument: There's no real detriment done to the game by allowing things like hens or pigs to be hitched to a post, or for Body Strength to be the limiting factor, and expanding the number of animals that can use it would make it more convenient to raise animals like pigs and chickens. Moreover, when a player attempts to hitch an animal to a post, it's not really clear why it would fail.
The realism argument: You can tie off damn near any animal to a post if you really want to. People even walk hens on leashes and harnesses (or you could tie a rope around its leg if you were desperate). It doesn't really depend on how strong the animal is, although it's obviously a bit trickier for smaller animals. Either way, it's certainly more obviously realistic than some other things we can already do with animals, such as hitching a giant insect to the yoke of a cart.
So basically... it's unintuitive on multiple levels why it works this way, and removing the Body Strength check would also improve gameplay applications without causing problems, so why not?