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.

"Good faith" is a difficult to grasp concept when concerning people who are holding your data for ransom

"good faith" == "continued future income".

There isn't any measure of morality or honor involved like you are suggesting.