1. Because of laws saying voting can only be done between certain dates (not too early, not late/after election day). You can argue what's wrong with voting too early, but voting too late should be a reasonable limit.
2. I dont understand it either, I always thought most military votes were republican.
My gut suspicion is because either #1 the people are stupid and just trying to reduce ballot counts (and increase the "bad ballot" totals) by any means necessary, or #2 the people are smart and advance polling has shown that while most military votes are Republican, the military has a lot more anti-MAGA GOPers so the net counts are probably Dem-leaning this year.