As an attorney, I think your second point is the most salient: the participants in a meeting at Amazon care even less than my clients would care about their smallest legal problem.

If you wait until the beginning of the meeting to prepare, there is an extremely high risk that someone else in the room is prepared to eat your lunch. Don’t surrender the initiative by being lazy.

Fwiw I bet Bezos pre-reads plenty of memos and I doubt very much that his is lazy. The point stands.