I would imagine for most, that money, and "other responsibilities" are the two biggest reasons. Most folks in the "middle class" have a limited amount of time and cash to spend these days.Priorities like the mortgage, vechicles etc, make spending a couple hundred dollars periodically a difficult pill to swallow, maybe taking the family out to dinner would come first. Single guys with more disposable, incomes are more likelly to be able to have the time and money to do things like this. Also many families may not be interested in spending their time together, shooting. My wife won't go, she used to, but has no interest anymore. I tried everything, she has no interest at all her hands are arthritic. So I either would have to go without her, or not go.Being that she works hard to keep us afloat, I would not feel right, even if I could go, other that the occasional hour or so, to function test, and stay somewhat sharp.
I think that 20 years ago I would have answered this question completelly different. When you are healthy and money is flowing, things are much easier.
I think that no matter who you speak to, these days, if they are retired or can't work or make what they are used to ,or unemployed. Things like gym memberships shooting frequentlly, restaurants, boats, even movies,replaced by "netflix" "blockbuster" and all the things that are not essential, go on the back burner. That's just life right now. Maybe if the economy comes back, more folks will get back in the pool.
I find that most of the guys who I shot with when I was younger 20-50, have either slowed down or stopped. And fixed income after retirement, makes plinking money down on a regular basis, tough.
Also many of us can't keep a schedual because of health reasons, or work.The same would hold true for any hobby or activity in these times.