Why have there been updates to the vanilla game but none to any of the DLCs? I realize the game was patched to accommodate them, but nothing to the DLCs themselves. The only fixes I see are unofficial ones on the New Vegas Nexus or elsewhere. I've fixed several issues myself (scripting and various other issues), but there are several that I don't know how to fix or that I haven't seen on the Nexus. I don't understand why Bethesda/Obsidian can't release updates for their own DLCs.

No interest.

Because to patch the DLC effectively, you have to reupload a whole new ESM with the fix integrated - modders can use esp plugins to make changes, but that option isn't available to the developers to use because of how unfriendly it is to the end user. Also because each patch plugin would have to get signed off on separately.

Which basically means you get DLC patches only in cases where the entire DLC is broke, ala the Pitt on release for the 360.