In that group I called the "smart poor" in my previous post, one can assume that every once in a while there is someone who possesses enough intelligence to learn about the world, to hear about such ideas as saving money, getting a real job, going to church, excercising, etc... Some of these individuals actually get tired of their life and they try to implement some change. This is where things get problematic. At first, any implementation of new strategies will be inherently wasteful, until the individual gets to a point where his circumstances, and therefore his incentives change.
I'm sure many who are not used to socio-economic arguments will stumble a bit here and say something like, "Isn't exercise good no matter who you are?" Well, physically it is good, but there are other costs involved. It takes time and money to exercise, and there also social pressures. At this soci-economic level, people are devaluing health in relation to those other costs for a reason. There's a much stronger commitment to exercise among those class who can afford gym memberships, team sports, various sorts of equipment, etc...
Thankfully, it still can be done. That's why the barrier is semi-permeable. The first condition is a change in mindset, the second is incurring a relatively high number of costs implementing new strategies, and third is when the new circumstances reinforce rather than erode adherence to those strategies. Hopefully, this sheds some light on why so few seem interested in doing much more than paying lipservice to real change.
Keep an eye out for the few.