There seem to be at least 3 reasons behind GB 2's change on this issue:
1. The GB are eager to inflate the flat growth rate in developed lands, and having the already associated youth baptized is an easy temporary solution. You can imagine how bad the newly baptized stat would look without this new policy. In a similar way they had already invented the "doorstop Bible study" to inflate the "Bible study" stat.
2. Several of the GB got baptized as children, and, in their eyes, it worked out well for them. People of limited thinking ability often cannot see outside their own realm of experience. We know how limited the current GB's thinking abilities are.
3. It is much easier to control the born-in youth if they can just DF them when they cause problems within the org. That way the org can marginalize any who act up and threaten any other born-ins with similar treatment. The easiest way for such a policy to work is to get the all the youth baptized early on as officially "in" and subject to the standard discipline, before puberty and its associated complexities hit.
What will be interesting to watch in the coming years is how the downside of this policy will play out. Should we not expect that there will be serious "loyalty" issues with moms and dads who went along with the new policy and had Johnny and Mary baptized at 9 or 10, and then Johnny and Mary went normal at 14? Would not such parents begin to say, "That was too young to get baptized. It shouldn't count!" after their kid is DFed at 14? The recent statements in a WT study article (as reported at this forum—I don't read them) about the permanent validity of baptism may well be indicating that this parental reaction is already hitting the fan...
I've thought about any biblical precedent that they might invoke on this matter. Not that I agree with it at all, but I suppose they might call upon the idea that in ancient Israel the youth were born into a commitment to keep circumcision, Passover, and the Mosaic Law, just by being an Israelite, because their ancestors had committed themselves and their descendants to do such things. Does anyone know if this as been espoused in WT publications on this child baptism matter? Of course, such thinking would fly in the face of the NT view, but I'm wondering if it's already been invoked by the org.