The only thing I can think of, as to why they might not do WDAs the week after release, is to analyze any player data (mods run/completed, completion times,deaths, fix any stuck character points, address any DM complaints/calls about little game breaking issues, etc.) and prepare to fix those in the soon to come Nerf-update.
None of those issues above don't come to light until the new mod hits, and aren't really on the previous WDAs. They might even want to keep half of the bugs/tweaks/exploits sorta "hush-hush", until a fix is prepped for the Nerf-update.