Why aren't all commands of the Prophet treated as obligatory?

Muslims are commanded by Allah(SWT) to obey Him and His Messenger without exception: > O you who believe, obey Allah, the Messenger, and those in command > among you. If you disagree about something, refer it back to Allah and > the Messenger, if you believe in Allah and the Last Day. That is the > best thing to do and gives the best result. > > **Surat an-Nisa`: 59** But I find differences in opinion among scholars on some issues whether it is obligatory or sunnah. Like in the case of shaving the beard: > Ibn 'Umar (May Allah be pleased with them) reported: The Prophet (ﷺ) said, > "Trim the moustaches and let the beard grow." > > **Al-Bukhari and Muslim **. Here the Prophet() is commanding as it seems from the text, but still there is a difference in opinion. Similarly, the below hadith also seems like a command, but most scholars interpret it as makrooh: > Narrated by Jabir bin `Abdullah: > > The Prophet (ﷺ) said, "Whoever has eaten garlic or onion should keep > away from us (or should keep away from our mosque).' > > **Sahih al-Bukhari 5452** So, the verdicts on whether a command by the Prophet is obligatory vary. How is this methodology of usool-ul-fiqh compatible with the Ayat above and other similar ayats in the Qur'an?