Living in rural Missouri has it's challenges when it comes to volunteer base for trail efforts. Urban areas have a much larger population to draw from and I've attended work days where there are 50+ volunteers.
In smaller towns, the same people that are generally "civic" minded and doing most the volunteer efforts are, more often than not, also involved in other volunteer efforts and have to plan their time between family, church, and civic obligations.
We aren't as organized as you may think. As large as this email list is, their is only a handfull that do most of the work. We have large efforts for our mega events like RIM, but most the time it is individuals taking care of a section and working around their schedules.
The key is to recruit new blood into the group so the work gets spread around. As others lose interest, it's important to find individuals that are enthusiastic and workers, not talkers.