This is a very challenging question primarily because it asks about natural dispositions in forgiving and no one knows the answer with certainty. My answer, based on reason, is open to feedback and change. I have three points to make.
First, I have never met a person who says, “Forgiveness is easy for me. It just seems to be part of my nature.” So, even if some people are better at forgiving than others, it still is not easy for anyone. In other words, even if one person seems to find it easier to forgive than others, that person still has an uphill struggle to become more perfected in the virtue. In contrast, some people with minimal practice do not find it hard to throw a baseball 90 miles an hour, although even this needs practice to achieve excellence.
Second, some people may find it easier to forgive than others because of what has happened to them “out there” in their family or community, as certain influential people show the person the way to forgiveness. The support from others could explain why some people have an easier (not an “easy,” but an “easier”) time forgiving than others. The person, then, might appear to have a natural disposition to forgive, but it has been made possible by others’ teaching and encouragement.
Third, there probably are certain qualities “in here” (inside the person) that aid a person in forgiving more readily and more deeply than others. Yet, it seems to me that those inner qualities, such as humility and love, are won only after a hard-fought struggle to advance in them. The developments, in other words, require much work and do not necessarily just happen, as can be the case with throwing a baseball at a higher velocity than the average person.
We all need work to advance as forgivers.