That's not a theory. It's objectively wrong nonsense. The bigger and better the splash you make at E3 the more coverage you get. That's how it works. If everything got drowned out and overshadowed then how would anyone get coverage? You make no sense at all. The best showings get the most coverage and the most boring showings get drowned out/forgotten.
Could you at least try to respond to anyone without coming across as insufferably passive-aggressive? The routine gets old after a while, is all.
Making a big splash costs money. Especially in an event like E3 where megacorporations like Microsoft and EA play. They pay people to cook up all their marketing, it's expensive as hell as sometimes costs almost as much as the game itself. If they think they can't/won't/aren't interested in making a big splash at that moment, they might want not to waste their ressources on something that won't get enough coverage for their investment. Thus, waiting on their own terms until they can make an announcement they think will have more bang for their buck. And give something minor in the meantime.
What interests EA is that the game has maximum coverage (and very preferably quality coverage) come release. That it comes at E3, Gamescom, N7 Day or anything along those lines is fairly irrelevant to them, I'd wager.
That's how I see it anyway. No need to jump down anyone's throat.