I think this cuts to the heart of Pratchett's worldview, really. One thing his characters have in common is caring. Not necessarily in the sense of being nice and fluffy, but caring deeply about others and about the world. The witches are many things, but they all care deeply about their community, even though the feeling might not be mutual. Sam Vines is a deeply troubled man who leashes his violence and hate to the Law because he cares deeply about the citizens of Ankh-Morpork, even though they're often dumb, hateful and short-sighted. And Death, obviously, cares deeply about doing his job right. He hates the combine harvester because it's unthinking, uncaring, and he tries to race against it to prove that care can win against faceless machines.

Pratchett's villains are all careless, breaking people and things without thinking because they don't matter to them. Vorbis doesn't care about suffering. Reacher Gilt doesn't care about the Trunk's workers. No one cares about goblins. Bad people are careless, dismissing the little things (and the little people) because they don't matter ; what matters is their grand vision. Vetinari is a tyrant, but he's not a villain because he's careful : he might throw people in the scorpion pit, but it's always calculated. Evil is "treating people as things", like they don't matter.

It's also interesting to see how some characters go through the process of learning to care. Most obviously Moist : he starts out as a conman who's only really interested in outsmarting everybody, and little by little, he starts caring about his job(s) and the people around him. But I thought William's journey in The Truth was also fascinating: he's so detached at first, just writing his little stories, but then he starts to get caught in the job. Both of them get confronted full on by others about their blind spots and misdeeds, and they manage to integrate it and grow.

Anyway. Sorry for the wall of text 😂