I can froward a few hypothesises, as to the lack of response.

• There are far more distractions as of late. Twenty years ago, computers were less powerful, and often built from kits - a bit less accessible then a book and a character sheet. Now its plug and play while RPGs require planning.

• Diffusion of responsibility - people tend to believe others will do it. If this was reason not to act in defense of the victims of violent crime (ie. Kitty Genovese) then being motivated for a hobby isn't too likely.
• We don't need cons to meet other players - so why go through the expense and crowds when my space (or this lab) will work just as well.

As to means of addressing these problems.

• start small - just your game group, then build up to 8-10 people, menstatize into two groups and an continue the cycle.

• Simply pick people or assign jobs. First aid training points out that being specific make people more likely to act.
• Offer means that aren't as readily available out-side a con - try to offer a raffle of a swap meet.

  There is a fine line between hobby and obsession. I seem to have lost sight of it some time ago.