The leading theory is that hardline hawks, who have been up in arms over the likelihood that Bush is going to conclude a deal soon with North Korea, somehow finagled the IC into holding the briefing as a way of stirring up trouble and making the deal less likely to proceed. Since hawks hate treaties of all kinds, and especially hate the prospect of a treaty with North Korea, this is plausible.
Still, something about it doesn't quite ring true. After all, the administration is pretty committed to working out a deal with North Korea before it leaves office, and although it's possible that Bush got outmaneuvered here, that wouldn't be my first guess.
However, there's another possibility: there have been some very credible reports recently that Israel and Syria are serious about trying to work out a deal of their own that basically exchanges peace for a return of the Golan Heights. The Bush administration is dead set against it. So maybe that explains the timing of the briefing. Maybe Bush figured it would stir up renewed hostility toward Syria and scuttle any attempts to pressure him into brokering a deal, but not stir up so much hostility that it would also scuttle ongoing talks with North Korea.
Maybe. It's just a guess. Daniel Levy has more along these lines over at TPMCafe.