Yes, I know you think that and you might be right, but Mueller's duty is pretty clearly spelled out under the law. He gives a confidential report to the AG. We don't really know what it says.
I don't think he's worried about his reputation, I think he is following the law. If he flouts the law what does that do to his credibility? I suggested a couple of weeks ago that Republican senators may be leery of signing off on a report without knowing what's in it. That's something that will play out over the next few weeks, but I don't think Mueller having a press conference and giving Nancy Pelosi a copy of a confidential report is necessarily a good move, either for him professionally or perhaps the country.
My belief is, it's out there, it will come out. Don't know when but sooner rather than later, IMO.