Easy. Crafted materials sell for more than the materials used to make them. I can turn 3000 in materials (damn xonolite) into an item I can sell for 16000.
If I watch the GTN for deals I can get materials prices down to 1500 and get over a 1000% markup.
Plus I only play a few hours a night in PvP then set all my alts to crafting while I sleep. So no farming for me; it's just something I setup while waiting for warzones to pop.