There is a difference between "absentee ballots" and "mail-in ballots." As I understand the way it works in most states, a person typically has to request an absentee ballot, verifying his or her identity and giving a reason that he or she cannot vote in person. Mail-in ballots were being sent out in vast mailings to many addresses for which there was not even any certainty that the person it was being sent to actually lived there. Then there was the fact that just about anyone could have filled one out and sent it in with no way of verifying who the person is. Mail-in balloting was thus rife with the kind of fraud we saw in the last election, fraud that is not usually found with absentee ballots.

Yes, absentee ballots are typically mailed in, but they are not what are referred to as "mail-in ballots." People have often conflated the two in their reporting, which is why some falsely accused Trump of hypocrisy, claiming that he himself utilized a "mail-in ballot," when he actually voted by means of an absentee ballot.

There needs to be a tightening of the language used when we refer to these votes, but I don't think those on the Left want this because constantly and falsely conflating "absentee voting" with "mail-in voting" more broadly works in their favor and allows the MSM to constantly misrepresent what is happening in a way that favors their narrative.