What is the wisdom behind the absence of a reason for the revelation of Surat Al-Fatiha, and must every Surah or Ayah have a reason for its revelation?

The wisdom behind the absence of a specific reason for the revelation of Surat Al-Fatihah or other surahs for which no reason for revelation is known, is not discernible. Some parts of the Quran were revealed for stated reasons, while others were not. Not every surah or verse has known reasons for its revelation. The reason for revelation might have been unknown to many Companions, or they might have differed concerning it. A verse might have been revealed for two or more reasons, or its revelation might have been repeated.