Individual announcements gives them more flexibility to make a schedule and don't put pressure on them to reveal content that is coming in 8 months or more and may not have a nice footage/information yet
Maybe they are testing this format to know whether individual teasers helps or muddle their AAA titles hype
To help B-list 3rd party games and indies they are still using Direct brand to they can get some spotlight, otherwise they would just pass ignored
I'm sure they will use Direct brand to very few big announcements, like a Switch New, Pro, Deluxe or whatever maybe early next year