Why was Al-Fatiha named "The Seven Oft-Repeated" (As-Sab' Al-Mathani)?

Surat Al-Fatihah was named "As-Sab' Al-Mathani" (The Seven Oft-Recited Verses) in the Qur'an and Sunnah, based on Allah's saying: "And We have certainly given you seven of the oft-recited verses and the great Qur'an" (15:87), and the Prophet, peace be upon him, said: "Al-Hamdu Lillahi Rabbil 'Alameen (All praise is due to Allah, Lord of the worlds) is the Seven Oft-Recited Verses and the Great Qur'an which I have been given." It was so named either because the worshiper repeats it in every unit of prayer (rak'ah), or because the worshiper praises and extols Allah with it, or because it was exclusively given to this nation.