The conversation regarding mail in voting seems to largely be suggesting that there will be widespread voter fraud (our side) and trump fears mail in voting because he will lose if it is allowed(their side)
But i think the reality is:
Dems know that without mail in voting, they are gonna get totally waxed.
The type of person that would "brave the elements" is decidedly more likely to be a trump voter.
The point being: without mail in voting, trump is an auto win. With mail in voting they think they have a fighting chance (they don't).
There is most assuredly an enthusiasm gap, people are willing to walk over hot coals, then drag themselves over broken glass during a billiard and hurricane happening at the same time to vote for Trump. Whereas the "enthusiasm" (if you can even call it that) for Biden is simply a "meh, if the lines aren't too long, then why not?".