What are you talking about? Small cities are just as rife with corruption. The nationwide "cash for kids" scandal occurred in a small city in Philadelphia. Pasco County, whose largest city is less than 20,000 in populace, literally collected lists of children's names and families for extra surveillance under the assumption they would be future criminals regardless of actual criminal history. Sundown Towns, a notion where hate crimes are effectively legal after dark, were enforced by local law enforcement (i.e. the law enforcement were lynching black people).

There's no reason not to believe that law enforcement everywhere can and does turn dangerous to the local population without stringent education, repercussions for bad behavior, and transparency.