@c Two things come to mind: 1. the online niche you are in is mostly Indiieweb so that skews the stats a bit, 2. micro posts don't attract native comments the way long essays would.

I look at native comments a bit like emergency flashers on your car: most of the time you forget they are there, but when you or somebody needs them they are vital. Akismet and AntiSpam Bee seems to keep most of the spam at bay for me but I don't have the volume of traffic you do.