The problem here is that these conflicts and preferences are constantly shifting. Two people can be good friends one week and decide they hate each others' guts the next week. And then they can go back to being friends again the week after. The Rosternator 3000 can't keep up with this so you're always going to be generating bad schedules for a certain portion of your people.

This is one of the reasons good retail managers ignore the advice of their time-keeping systems and give peoples' requests preference. The time-keeping system ignores all of the human aspects of the problem to focus on the least-important aspect of keeping a store running--making sure there are warm bodies in it.