Why do business laptops still have trackpoints?

Because there are still a few that do like to use them

First, Trackpoint is a proper noun trademarked for the Lenovo Thinkpad pointing stick. Second, the Thinkpad ones operate smoother and more accurately typically. Third, in choices of an external mouse, touchpad, or Trackpoint, external mice are usually considered best but not a portable, then Trackpoint, then touchpads. There are people that buy Thinkpads BECAUSE of the Trackpoint, and with the trademark status to give a distinctive appearance, they do not go away soon.
They pulled it from the 11e little Thinkpads. They are also not on the cheaper B series Thinkpads.
People that don't want to use it don't have to, as they all have the same touchpad that competing systems have. It is an extra feature.