Why is Mary needed as an intercessor?
Perhaps that's tackling it the wrong way round. Granted that He had a Mother, why wouldn't He honour her? Why wouldn't He take her intercessions seriously? And on a more abstruse theological basis, surely He was "obliged" to include in His scheme of Providence the intercession of His Mother — and His foster-father for that matter — if He was to be incarnate at all. In the same way, & not being silly, but illustrating the point: granted he was to be incarnated, He "had to" have an actual Mother who was a real woman. Joseph was apparently dead before His public ministry began, but in His 30 years in Nazareth He was not only obedient, but the Gospel says: He was subject to His parents. He supernaturalised family life, He did not sweep it aside for Himself. Indeed, on the theological level, we could say that the Holy Family is the "Real thing" - the Archtype — while our Natural Families are only imperfect copies — "ectypes".