I don't think exactly that happened. I think Mueller is operating in the Justice Department's "can't indict a sitting President" space. So he presented all the evidence about obstruction of justice for congress to use if they want to impeach Trump. From that perspective, that's where prosecution for those crimes belongs.
We are now hearing that some members of Mueller's team are unhappy with Barr's summary letter, since they already wrote summaries. I think thus is probably because Barr only got the job because he said that Presidents can't obstruct justice, and there is good evidence in the whole report for obstruction of justice charges. Barr has not released those summaries from the report most likely because they say that the President should be charged.
