This isn't like WoW where you hammer a mining opint once and get 50 ore. Materials are limited. Most people purchase items specifically for their needs. I may give a couple nuggets or sinew to someone if he or she wants to synth that for a craft, but I'm not going to give crazy materials to people. Although I receive crazy materials, heh. And gil is too easy to come by and you can't fully repair your equipment from an NPC. At our current state, linkshell banks wouldn't give any long lasting benefit. Maybe one day in the future it will be very beneficial, but right now, I don't think it would be too helpful.