It was already explained to you why he did not state his personal conclusion. Read post #360.
Why did the investigators and Mueller include the following?:
“Mueller added that the President "does not have immunity after he leaves office" and that his team "conducted a thorough factual investigation in order to preserve the evidence when memories were fresh and documentary materials were available."”
After making a “thorough factual investigation” into these matters, the Special Counsel considered whether to evaluate the conduct under Department standards governing prosecution and declination decisions but ultimately determined not to make a traditional prosecutorial judgment. The Special Counsel therefore did not draw a conclusion — one way or the other — as to whether the examined conduct constituted obstruction.
"Our investigation found multiple acts by the President that were capable of exerting undue influence over law enforcement investigations, including the Russian-interference and obstruction investigations. The incidents were often carried out through one-on-one meetings in which the President sought to use his official power outside of usual channels. These actions ranged from efforts to remove the Special Counsel and to reverse the effect of the Attorney General 's recusal; to the attempted use of official power to limit the scope of the investigation; to direct and indirect contacts with witnesses with the potential to influence their testimony. Viewing the acts collectively can help to illuminate their significance. For example , the President 's direction to McGahn to have the Special Counsel removed was followed almost immediately by his direction to Lewandowski to tell the Attorney General to limit the scope of the Russia investigation to prospective election-interference only-a temporal connection that suggests that both acts were taken with a related purpose with respect to the investigation."
"Many of the President's acts directed at witnesses, including discouragement of cooperation with the government and suggestions of possible future pardons, occurred in public view. While it may be more difficult to establish that public-facing acts were motivated by a corrupt intent, the President's power to influence actions, persons, and events is enhanced by his unique ability to attract attention through use of mass communications. And no principle of law excludes public acts from the scope of obstruction statutes. If the likely effect of the acts is to intimidate witnesses or alter their testimony, the justice system's integrity is equally threatened."
"The President 's efforts to influence the investigation were mostly unsuccessful, but that is largely because the persons who surrounded the President declined to carry out orders or accede to his requests."
“If we had confidence after a thorough investigation of the facts that the President clearly did not commit obstruction of justice, we would so state,”
and a big ones:
"Under OLC's analysis, Congress can permissibly criminalize certain obstructive conduct by the President, such as suborning perjury, intimidating witnesses, or fabricating evidence, because those prohibitions raise no separation-of-powers questions." Page 382
"With respect to whether the President can be found to have obstructed justice by exercising his powers under Article II of the Constitution, we concluded that Congress has the authority to prohibit a President's corrupt use of his authority in order to protect the integrity of the administration of justice."