Many Codexers in denial about this.
The thing is their "side story" sucks balls
The entirety of Through the Ashes has less story content than Chapter 1 of the game base game and is just as long due to sort of puzzle like gameplay. Not to mention the characters ended up being incredibly bland and the whole campaign reeks of wasted potential.
Varnhold's lot while excellent is once again like 85 - 90% dungeon crawl. The tavern + werewolf thing was nice and I wished they could take its quest design to the future (they don't, mostly) but once again most of the plot are flat once you step in the mega-dungeon.
It's not surprising that player prefer to play main content because as designed the side-stories feels like a chore. Too short to feel meaningful, too long without meaningful content.