I'm not an admin or mod, so I don't know for certain, but I do have a theory. One thing that seems clear to me in the creation of the new site and forum is that they (the admins and mods) appear to be moving away from Star Wars LEGO specifically and more to LEGO in general. We see this in the creation of the different LEGO forums and in the consolidation of the MOCs forum.
To that end, given that Star Wars software was basically on the fringe of Star Wars LEGO already (the only real link being the aging Star Wars LEGO videogames), discontinuing the forum related to it seems in-keeping with the new focus of the site. Also, when it comes to LEGO software, there really isn't that much to talk about, and they could easily fit into the expanded LEGO boards.
Now, some may disagree with the desicion to discontinue discussion of videogames. Lord knows I butted heads with the mods in the past over the extremely-cramped videogame thread in the old BCS. However, I'm beginning to agree with mods on this point (
Shocking, I know). The focus of this site is LEGO, not videogames. While there is room for discussion in the BCS for such things (to a limited extent), it just doesn't really fit the site to do much more than that.
And I bet you mods thought I would rant about how a new forum should have been created for videogames. Not today, guys, not today.