A sheriff is the highest law enforcement officer in a county and is also responsible for maintaining order and enforcing laws.
There are many reasons why someone would want to run for the office of sheriff. They might want to improve their community by enforcing the law, they may want to help ensuring public safety, or they might want to serve their community and protect it from crime. They may also have a deep understanding of criminal justice system and they believe that they can make a difference.
Why someone may run for office may also have to do with a particular issue that the sheriff candidate will make as part of their campaign platform.