TL;DR - all the reasons that make computers efficient makes efficient corruption more possible.<p>i.e. the inefficiency of the manual, physical process is a feature--being harder to corrupt/DDoS.
The gold standard is Australian Ballot -- private voting, public counting -- cast at poll sites, immediately tabulated when polls close, then results posted publicly.<p>Just a TLDR. There is so much more. Election administration is pretty involved.<p>Electronic voting breaks the Austalian Ballot in two ways.<p>Whereas a ballot box protects voter privacy by being a secure one-way hash (physical shuffle), all electronic systems record the order ballots are issued then cast (necessary for auditing).<p>Electronic voting also obliterates the physical chain of custody.<p>FWIW, to protect privacy, postal ballot processing has to properly batch (by precinct) before opening. Your jurisdiction probably doesn't do this, due to cost and timeliness.