I think it's because--and this is hardly uncommon--LA Noire's flaws become increasingly apparent over time. A huge part of the game's appeal is the striking first impression achieved by the technology, but that initial wow factor only lasts for so long. What you're left with, then, is the design of the game itself, which is much more ambivalent.
I think you'll find, for instance, the GB crew will be much cooler on the game as we approach GOTY season, with the possible exception of Brad, who will inevitably be put in the position of having to defend his review.
What a bizarre turn of events. No idea what to think at this point. While I'm finding it easy to ignore the existence of C&C: Generals 2, I don't like the prospect of the Bioware "brand" losing all semblance of value. Mark me as concerned.