Microsoft keeping developers quite about future PS4 titles? (metal Gear/Battlefield)

[teigaga]

SunofKratos said:
Many developers will simply wait until e3 before they anounce there next gen games. I think there is no doubt that Battlefield 4 came to PS4 and X Box next too.

But why would they wait to E3 when the game is expected to come out for next systems anyway?