He also gets to keep himself at the public trough for some more time. Mueller is not doing this for free even though he is old enough to be getting his gov’t pension. (Which is a couple of good questions)
I don’t deny what you are saying, but once again it goes to whether this is in pursuit of a conviction, or personal gain.
Money or a pardon would not be in pursuit of a conviction. It could only be seen as a bribe.