I see this come up a lot in discussions about voting in America. Postal votes disproportionately go to Democrats, hence the Democrats want to expand postal voting while Republicans want to restrict it (and insist there is totally a bunch of fraud going on).
I’ve googled with a few search engines and haven’t found a convincing reason. Lots of evidence that the skew is real, but no explanation as to why. Indeed, if one just looks at demographics, one would expect postal voting to benefit Republicans by facilitating votes from people in the countryside who live far away from voting centers.
So what actually gives?
When you can control where the polling locations are, you can drastically under serve areas that don’t vote republican. This discourages or even makes completely impossible voting in some areas. I live in a wealthy republican suburb. In the last 25 years there has never been much of a line to vote at any time of day. I can usually get in, vote, and be out in 15 minutes. Within a 20 minute drive of me, there are polling locations that have lines which take many hours to get through. Many people have to take time off of work, or leave their kids home alone to vote. Some people can’t stand in line for that long due to health issues.
While mail in voting enables traveling businessmen, college students, military, the elderly and sick to vote - which probably doesn’t overly favor either party - it does disrupt the polling location engineering which is intentionally designed to favor one party over the other.