What are the reasons upon which the Hanafi school relied to say that raising the hands when bowing and rising from it is not a Sunnah, and to suffice with raising them only for the opening Takbir, and is this the view of Imam Abu Hanifa or an ijtihaad (independent reasoning) of his followers?

It is established by the continuously transmitted Sunnah from the Prophet, peace and blessings be upon him, that he used to raise his hands at the opening takbir (takbirat al-ihram), and when saying the takbir for bowing (ruku‘), and when rising from it. The ten (narrators) have agreed upon its narration, and nothing contrary to that has been authentically reported from him. It is possible that Imam Abu Hanifa was not informed of this hadith, or he was informed of a weak hadith that stipulated no raising of hands except for the opening takbir.