Insulation around gas lines?

I tore out the drywall to install backer board for a faux brink finish. When I took out the drywall I was sureprised to not find any insation between the outer brick wall and the drywall. The home's natural gas does run between that space. Is there any reason why there is no insulation between the eterior brick wall and the old dry wall? Also. Am I safe to layer some insulation over the gas line between the interior drywall/backer board?