[cameldrv]

In the specific measures of civic organizational membership, you have to put a lot down to women entering the workforce. People of my grandparent's generation (middle aged in the 50s and 60s) participated heavily in these activities, Elks and church in their case. A lot of the planning and organization of these groups was done by women who stayed home. Particularly after the kids had gone off to school, homemakers put a lot of effort into civic groups during the day. Now, of course, there were lots of women who worked, but there were enough women who didn't to keep these groups running. With women staying home now rare, especially after the kids are old enough for school, the people with free time to keep these organizations going don't exist. If you want to see a subculture where these organizations are still thriving, look at members of the LDS church.