All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If what is meant by your question is why we do not call Abu Haneefah by Imaam Abu Haneefah when mentioning his name, then there is no doubt that stating this term (i.e. Imaam) when mentioning people like Abu Haneefah and other scholars is something required as this is a way of honouring and respecting them and attributing for them the honoured status that befits them. However, this is not a religious obligation because, for example, we say Abu Bakr and 'Umar without mentioning the term 'the Prophet's caliph' or 'the leader of the believers' before their names. So, this is a relaxed matter that should not be taken so sensitively.
However, if you are asking why Abu Haneefah was called by this name, then the answer is as follows.
The name of Abu Haneefah is An-Nu`maan Ibn Thaabit Ibn Zawti At-Tameemi, Al-Kufi. He was born in 80 A.H and it was said that he met Anas Ibn Maalik . It was also said that he met seven companions . For more benefit, please refer to Fataawa 86509 and 88718.
Furthermore, it was said that he was nicknamed Abu Haneefah because he used to always carry a Haneefah, a word which means an inkpot in the popular Arabic language of
As regards the authoritative books which reported his biography in details, there is Tahtheeb Al-Kamaal, written by Al-Mazzy who wrote approximately 30 pages about his biography mentioning his merits and the praises of the scholars about him.
Moreover, Ath-Thahabi wrote a book about the merits of Abu Haneefah and his two close companions, entitled: "The Merits of Imaam Abu Haneefah and his two close companions" who were Abu Yoosuf and Mohammad Ibn Al-Hasan. Besides, Mohammad Ibn Yoosuf As-Saalihi, from the Shaafi'ee School of jurisprudence, wrote a book about him entitled; ''The Merits of Abu Haneefah An-Nu'maan.''
In addition to this, some books were authored in this century defending him; some were written to defend him against Ibn Abu Shaybah, and some were written in defending him against Al-Khateeb. The most important of these books is the PhD dissertation written by Doctor Mohammad Qaasim 'Abduh Al-Haarithi, entitled: ''The Status of Abu Haneefah among the Muhadditheen (compilers of Prophetic narrations).''Allaah Knows best.