Dave, I feel like I've come to "know" you reasonably well over the past few years.......at least as well as a cyber familiarity will support. Most of the comments above advance legitimate observations, and with each additional post more factors can be added. It must be some part of human nature to seek "the reason". We hear it frequently when someone wants to identify causes for concerns, they'll say something like "THE problem is...............". But I think it's more a range of things than any single factor.
I agree with your basic premise to some degree, probably moreso than not. But in part the concern comes from your and my unmet expectations..................and when we perceive a "problem" it means our expectations are out of line with reality. I suspect for we older guys who no longer have a work environment to provide mental stimulous, we seek a substitute. We're no longer in the intense input environment that our former career process imposed on us.
Like you I'd like to see more exchanges that interest me here, but that's not happening so I just take what comes along. Are we suffering another National malaise? Yeah, and it impacts a lot more of human interaction than I think most people realize. Hang tough, keep seeking fulfillment, it will appear in time if you keep at it.