I imagine it partly comes down to wanting things to talk about at E3, but also I'd imagine that, for the investors, Directs just aren't "worth" it. Look at their financial scenario and the sales of their latest systems. It would seem as though these directs; whilst good for fans; aren't helping the sales of their system.
So I imagine they're going to wind down the formal into having directs about individual games only eventually, and make announcements throughout the year as other companies do.