The lifecycle do get interrupted with early voting and postal voting, and as past elections where I live have shown (Sweden), some number of boxes of votes will

The lifecycle do get interrupted with early voting and postal voting, and as past elections where I live have shown (Sweden), some number of boxes of votes will generally be discovered after elections. The postal system are not designed to be 100% reliable and some portion of mail do get lost, fail in the sorting process, or get sent to the wrong location and put into the "fix it later" process which will miss the election deadline. Software and hardware is still magnitude more vulnerable to intentional misbehavior, and even accidental mishaps has a higher risk of massive negative consequences, and its harder to discover failure compared to boxes of votes that has a physical presence.