Roman sculpture was influenced by Greek sculpture. They copied techniques of the Greek sculptors and developed it in their own style. The Roman art style was highly veristic; on the other hand Greek art was idealistic. I have two theories why Roman sculptors were so much in to verism.
First, Romans did not want to leave the history of stealing or copying ideas and styles of Greek’s art. That is why they tried to focus on verism so as not to look like Greek art. And also they wanted to make something new and make something that can be compared to Greek art. Roman looked at Greek as a good model for example, but also rival.
The second theory is that Greek art, which focused on ideal style were stale for Romans and did not interest them. Romans may had been interested in technique of Greek art, but they had different taste for art. Their interest was more in accuracy and precision. That is why they did not make sculpture of godlike beautiful people like Greeks did. I like the way Romans did for sculpture because we can see simple and average people. And also, it is more emotional.
They may have wanted to leave what exactly Roman culture, people, thinking, and what their life was. That is why verism was so important for Romans.To conclude this, those two theories were why verism was important to Roman; to not leave history of copying and they wanted to leave who exactly Romans were.