Romans embraced verism in their art. They portrayed people as they were rather than idealistically as the Greeks did. This realistic approach to art was unique at the time because many other cultures had canons for the human form and would always make important people flawless in artistic portrayals.
The accurate documentation of a person’s features in Roman portraits revealed certain personality traits and qualities that give viewers a truer idea of who the person was than a god-like, youthful portrait. Romans learned from their history, so keeping records of their history was important to them. They were not interested in perfection or idealism but truth because they learned from it. Because they valued history, I believe this is one reason why verism held importance in their art.
Romans were also doers. They were not, for the most part, philosophers as the Greeks were. They had a much more straightforward and realistic approach to life, another aspect of Roman culture that appears in their art.
Their value for family also may have played a part in their fondness of verism. It was a way to preserve an accurate memory of a person long past their death. I do not think this could possibly be the only reason or even the main reason they valued verism because family was valued in many other cultures as well and it doesn’t seem to result in massive amounts of realism in art history.
Roman verism probably stems from several cultural reasons. Their values make them appreciate truthful portrayals of people.