VPs salute the military members stationed outside Air Force One and Two whenever they board and disembark the aircrafts. It's just what they do.
Kamala Harris, however, does not. And it's really weird and awkward and obviously calculated.
Look at these videos:
This one's from Monday:
Look how flagrant that is!
Here she is disembarking Air Force One with President Biden. This is how you know it's calculated. Biden salutes them all, and she watches him do it. Then she proceeds to, y'know, not: