The land that gives us cool rocks, fast soils, banked turns and undulations in the trail. If not for the dirt we wouldn't be mountain bikes and we would never catch killer air of ledges and make great tech moves. Hey, we can all see the attraction in the freeride craze, cool riding on cool dirt. So that is why advocates speak up. In part for the dirt, in large part to preserve the sport, the way of life, we love so much.
Some advocates work in politics fighting for trails.
Some work in local clubs working with land managers and local riders. Others, to me the silent heroes, work in the dirt. They repair the damage others do. They try to educate riders to the way of low impact riding. They also build trails, the single best way to keep all impact in one small place, and maintain the trails that exist.