Execution. nuBSG just had that feeling of juvenile posturing built into it.
Plus - and I say this as someone who didn't watch for about 3 years in a strop over such posturing - when I did get absorbed again into BSG the ongoing narrative was huge and compelling with a great variety of characters (Cavill could steal a seen).
Walking Dead just has bleak character after bleak character.
I did make mid-season three finale, but am officially over it now. I just had the last couple in the background while I did other stuff. Whereas I was trying to hold together some interest, I gave up on even that pretence.
As to Andrea... ironically she's the character I felt quite drawn to, and cared about... but that disappeared this season since all she did was look quizzical.