Structural theorists do not tend to focus much on middle class crime. They tend to discount it, saying that middle class crime is less important than lower class crimes. This is in part because lower class crimes tend to be more violent than middle class crimes.
To the extent that structural theorists do focus on middle class crime, they might attribute it to structural weaknesses in the community and family. They would argue that even middle class communities today are less cohesive than they once were. The rise in ethnic diversity could be partly responsible for this. So could the rise in mobility among Americans. Both of these lead to neighborhoods where people do not know one another well and cannot exert social control over one another. Another factor would be the decline in the strength of American families. All of these structural changes have reduced the level of social control that can be exerted over people, even in a middle-class, relatively privileged setting.
Structural theorists of crime might take a number of different approaches to middle-class crime. First, they might focus on the stability of life in the middle class, financial stability in particular. In the United States, for example, they could look at changing standards of living, the likelihood of remaining "middle class," or perhaps the definition of "middle class" in a given society. Some factors they might investigate could include the gap between middle class mores and cultural expectations and realities. They might look at the challenges of maintaining a middle-class lifestyle, and how some might be driven to certain crimes in order to maintain that lifestyle. Moreover, they might look at how some middle-class youths in particular rebel against the confining morality of the middle class. This, in fact, was a major trend in the United States at various points in our history, perhaps never more than the 1950s and 60s, when middle class youths embraced first a culture of juvenile delinquency and then a counterculture in opposition to middle class values.