Now that you mention it, I see the trend you pointed out. Over the years I have posted quite a few stories/novels here and had two of them go on to be published, giving credit where credit was due on the Acknowledgements page to those who helped greatly in the success. Beginning early this spring, the level of readership/reviews did seem to drop off. I must include myself as a glaring example of this phenomena however. I've been a total sloth in reviewing as much as I had before. Instead, I find all sorts of excuses to keep from logging in and commenting/reviewing. For that I apologize. I like your phrase "drive-by comments" as it accurately describes many of those I have seen on other's posts.
I have been involved in an ongoing personal health and family struggle, but can now see the light at the end of a very long, dark tunnel. In the past nine months or so I've hardly touched pen to paper, so to speak, and my work on my latest novel, a sequel, has suffered. I hope I will get my act together, overcome my massive writer's block, and continue as before: reading, reviewing, chatting in a forum, and generally returning to this site much more often than I have been lately.
Bill