They tend to ban bots in waves. They don't want them to know what activity specifically got them banned I believe. They're part of the report you see on the lodestone every so often for Actions Taken Against In-Game RMT & Other Illicit Activities. For example Jan 5 - Time Period: Dec. 22, 2016 to Jan. 4, 2017

・Accounts receiving disciplinary action for RMT advertising: 1,232
・Accounts receiving disciplinary action for RMT/illicit activity: 47,989
・Action Details: Permanent ban from FINAL FANTASY XIV

the bots would fall under "illicit activity". However, as soon as a bunch of bots are banned, more will be created. The stuff they gather is sold on the Market Board and then the gil is prob used to sell to players buying into RMT.