He filed his $50M report and left it to the AG and Congress to act, or not act, on its contents.
His job was done, and he did not want to testify publicly.
Power-mad Democrats, desperate for impeachment, staged the hearing.....even handed out talking points.
They wanted Mueller to recite for the TV cameras every charge against the president.......a public recital of Trump's sins (as they see them).
But thanks to alert Republicans, America saw a humiliating spectacle, indicting both Mueller and Democrats.
Three stooges and a moron.