While mounted, right clicking on a hitching post should make the rider move towards it and automatically hitch the horse to it, permissions allowed of course.
The process of dismounting, selecting a rope from the inventory, chasing the horse (which loves to roam off immediately after dismounting), then actually hitching them to the post, then returning the rope to the inventory, all seems excessive.
I see a lot of people (myself included) not bothering with hitching posts because it's easier to just hunt down the wandering beasts later. Just seems like a little convenience thing that would make the process much more intuitive.