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?
Republican voters skew older (retired) so if you make voting difficult for people, the ones with more free time are the ones more likely to vote.
The easier it is for everyone to vote, the less the Republicans are favored.
Mail in ballots would also favor rural voters but I guess there are not enough of them for the conservatives to worry about?
But in short - no, the mix of voters does not stay the same as it increases.