There is no national agency that administers American elections; they are overseen by more than 10,000 local jurisdictions. With each state and local government running elections and counting ballots, often with the help of citizen volunteers, mistakes can happen. The cost of holding elections is paid from local tax revenue, so local governments have a disincentive to invest in upgrading voting systems. In 1993, in the interest of convenience and increasing turnout, Congress passed the National Voter Registration Act, also known as the Motor Voter Act.”]
Source: https://gcn.com/articles/2018/10/15/challenges-accurate-vote-counts.aspx