Because it's just much more pleasant to use. Plus, being able to manipulate the mouse without taking my hands off the keyboard is also a big advantage.
I've never used a trackpad that did not have at least one of: bad palm rejection, inaccuracy around the edges, clicking that feels bad and/or makes the mouse cursor drift while trying to click.
Granted I have not used an expensive, modern laptop in a while and it could be much better now, but even then I just think the trackpoint is better UX and better posture, there's something uncomfortable about having to awkwardly squish your arm between you and the laptop to manipulate the cursor.
I've never used a trackpad that did not have at least one of: bad palm rejection, inaccuracy around the edges, clicking that feels bad and/or makes the mouse cursor drift while trying to click.
Granted I have not used an expensive, modern laptop in a while and it could be much better now, but even then I just think the trackpoint is better UX and better posture, there's something uncomfortable about having to awkwardly squish your arm between you and the laptop to manipulate the cursor.