Busy  - we read and run 
Possibly related to busy - too tired/lazy to think of something to say ? 
Or maybe we just forget that a lot of (volunteer) effort goes into maintaining a blog, especially one of this caliber, so we take the flow of information for granted and don't think about adding feedback.  And by feedback I mean comments/conversation about content.  Know that one should never speak for anyone else,  but feel pretty confident in saying KC is looking for input not thank yous. 
Those things wandered through my mind because they all apply to me . . especially the second one.  Putting thoughts into coherent sentences doesn't come easily to me, so if I'm in a hurry or tired it's easy to tell myself I'll do it "later".

On another note . . you probably have a point re: competition.
A board ( no GPN connection ) I mod for is nearly dormant.  Ironically more has  happened in the last 6 months than during the previous 2 years, however new threads get views but few if any comments.  Yet almost all of our previously most active members can be found on Twitter nearly every day - including us, the board's staff.  We can draw a time correlation between increased activity there and reduced visits to the board .. the "whys" are just speculation.