It is not true that Lord Shiva isn't referred to as the father.
In Adi Shankara's Annapurna Stotram itself we find one such reference:
क्षत्रत्राणकरी महाऽभयकरी माता कृपासागरी
साक्षान्मोक्षकरी सदा
शिवकरी विश्वेश्वरश्रीधरी ।
दक्षाक्रन्दकरी निरामयकरी
काशीपुराधीश्वरी
भिक्षां देहि कृपावलम्बनकरी मातान्नपूर्णेश्वरी ॥१०॥
Kssatra-Traanna-Karii Mahaa-[A]bhaya-Karii Maataa Krpaa-Saagarii
Saakssaan-Mokssa-Karii Sadaa Shiva-Karii Vishveshvara-Shrii-Dharii
|
Dakssaa-Kranda-Karii Niraamaya-Karii
Kaashii-Pura-Adhiishvarii
Bhikssaam Dehi Krpa-Avalambana-Karii
Maata-Annapuurnne[a-Ii]shvarii ||10||
Meaning:
10.1: (Salutations to Mother Annapoorna) Whose Great Power Protects the Devotees and grants them Great Fearlessness; Who is the Great
Mother and an Ocean of Compassion,
10.2: Whose Divine Form is a Visible bestower of Liberation and Whose presence always brings Auspicious blessings; Who is indeed the
repository of the Sri (Prosperity, Welfare and Auspiciousness) of
Visweswara (Shiva),
10.3: Who makes Daksha (symbol of ego) Cry and in that repentence makes him Pure; Who is the Ruling Mother of the city of Kasi,
10.4: O Mother Annapoorneswari, Please grant us the Alms of Your Grace; Your Grace which Support all the Worlds.
अन्नपूर्णे सदापूर्णे शङ्करप्राणवल्लभे ।
ज्ञानवैराग्यसिद्ध्यर्थं
भिक्षां देहि च पार्वति ॥११॥
Annapuurnne Sadaa-Puurnne Shangkara-Praanna-Vallabhe |
Jnyaana-Vairaagya-Siddhy[i]-Artham Bhikssaam Dehi Ca Paarvati ||11||
Meaning:
11.1: (Salutations to Mother Annapoorna) O Mother Annapoorna, You Who are always Full (with the gift of Food and Blessings), You Who are the
Beloved of Shankara, ...
11.2: ... O Mother Parvati, Please grant me the Alms of Your Grace, to awaken within me Spiritual Knowledge and Freedom from all Worldly
Desires.
माता च पार्वती देवी पिता देवो महेश्वरः ।
बान्धवाः शिवभक्ताश्च
स्वदेशो भुवनत्रयम् ॥१२॥
Maataa Ca Paarvatii Devii Pitaa Devo Maheshvarah |
Baandhavaah Shiva-Bhaktaash-Ca Svadesho Bhuvana-Trayam ||12||
Meaning:
12.1: (Salutations to Mother Annapoorna) My Mother is Devi Parvati, and my Father is Deva Maheswara (Shiva),
12.2: My Friends are the devotees of Shiva, and my Country is all the Three Worlds (Whose Lord is Shiva-Parvati).