There's always an incentive to run with this thing- taking down a president brings with it a huge reputation. So guys are tempted to stick with such an investigation, long past the obvious time to put this away.
Then, there's is also D.C. Mueller is in D.C. He likes to deal with D.C. people. He probably knows he'll get many kudos from other D.C. people who don't want the swamp drained.
But Mueller also ought to want to do the right thing, which is stop this fucking circus. Of the ten thousand investigations that need to be going on in D.C., this is not one of them.
By doing the right thing Mueller can also become that one guy Trump, Sessions and others will trust. Is that a good idea in D.C.? I suppose it depends on who you think will win. If Trump loses, it will because he was timid. He keeps trying to behave himself. He consults with lawyers. He hasn't thrown large numbers of bureaucrats in jail- which is practically necessary. You can't stop a criminal conspiracy while the conspirators are in charge of things, and you can't know who specifically is criminal until they are all vetted.
Kind of sucks, but, we are seeing this crap now. The Russia thing is dead, warmed over twice. And yet, supposedly, the investigation is widening, even unto obstruction of justice. Just how stupid do these people think we are?
Which brings me back to Mueller. Perhaps these idiotic journalists are doing him a disservice. He has a choice, and it should be to end this damn nonsense.
Perhaps he will, assuming he realizes his own reputation is at stake here.