Just to illustrate the 2nd point using Barr's letter

"the report sets out evidence on both sides of the question and leaves unresolved what the Special Counsel views as “difficult issues” of law and fact concerning whether the President's actions and intent could be viewed as obstruction. The Special Counsel states that “while this report does not conclude that the President committed a crime, it also does not exonerate him.”

The reason that Trump was not indicted for obstrution of justice was because the difficulty of assessing his state of mind.