Aren't they all anonymous, though? So they could just change their name for the next operation. Maybe all these groups are already the same people behind the scenes.
You're missing the incentives. They /could/ change their name each operation, but then, as you note, the target would have reduced motivation to actually pay. By keeping their name, and keeping their word, customers are more likely to pay in the future, because there's a history of good faith transactions. And, of course, a group that is relying on their reputation like this must police their trademark and prevent other groups from abusing it.