Why did not Sage Vyasa praise Ganapati in the opening shloka of the Mahabharata?

According to my understanding, Gaṇapati was not Rig Vedic God, though Rig Veda 2.23.1 mentions Gaṇapati.

ग॒णानां॑ त्वा ग॒णप॑तिं हवामहे क॒विं क॑वी॒नामु॑प॒मश्र॑वस्तमम् । ज्ये॒ष्ठ॒राजं॒ ब्रह्म॑णां ब्रह्मणस्पत॒ आ न॑: शृ॒ण्वन्नू॒तिभि॑: सीद॒ साद॑नम् ॥

However, Gaṇapati mentioned in Rig Veda 2.23.1 refers to Brahmaṇaspati/Bṛhaspati, but not the son of Uma and Shiva.

Gaṇapati as the son of Uma and Shiva is a Puranic god. Further, Puranas were composed, as per prevalent stories, after completion of Mahabharata by Sage Vyasa..

Hence, appearance of Gaṇapati in the opening chapter of Mahabharata is an interpolated version.

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We have to remember that the estimated period of Mahabharata is around 3100 BC. And, Sage Vyasa could not have prayed to Gaṇapati.

Further, even the opening shloka - नारायणं नमस्कृत्य ,might have been incorporated at a later date, as the tradition prevalent at the time of Sage Vyasa was to follow DHARMA.

नारायणं नमस्कृत्य नरं चैव नरॊत्तमम
देवीं सरस्वतीं चैव ततॊ जयम उदीरयेत

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Even in the Surya Siddhanta, a text composed in 5–6 Century BC,the author starts with a prayer to formless BRAHMAN or ENERGY.

अचिन्त्याव्यक्तरूपाय निर्गुणाय गुणात्मने।

समस्तजगदाधार​-मूर्तये ब्रह्मणे नम​:॥

To him whose shape is inconceivable and unmanifested, who is unaffected by the qualities, whose nature is quality, whose form is the support of the entire creation—to Brahma be homage!

Hence, Sage Vyasa, who lived much before the author of Surya Siddhanta, might have prayed to formless BRAHMAN.