Sunk cost fallacy on my end as well.
I also don't want to lose my houses (Personal and FC), so I log in often enough to keep them going in case I get the sudden urge to actually play for once. I go through peaks and troughs with this game, so I'm hoping this is just a bit of a slump and I'll find the spark again sometime, but this expansion has been a low point for me. When I do play I hunt for achievements mostly or do old side content that I never really bothered with first time around like PotD and HoH.