Couple things... First, if the GMs took the time to respond to every single bot/rmt report, they'd never have a chance to do anything about it nor handle any other situation. Second, the GMs are not as concerned with identifying the gatherer bots (or even the RMT bots) as they are the 'mule' characters holding and moving the gil around.
To be honest, SE might even see this type of activity as a way to REMOVE excess currency from the game as a gil sink. If you buy shards/crystals/clusters/materials from a RMT gatherer bot, and that gil gets put on a mule character, and then that character gets banned they have effectively removed potentially millions of gil from the economy which can actually help cut inflation and keep the market stable. It's sad if the economy is that unbalanced for that to be a possibility, but there you have it.