The first church dedicated to to the Virgin Mary was built after a Church council declared her to be Theotokos. Which is to say that her son Jesus was true God and true man. Mary is revered because she is the first among all us creatures of God, because her son is NOT a creature, the son of God, though like us in all ways except sin.
Mary is revered because She is the perfect example. There is no human who has shared a closeness and unconditionally loved Jesus like His mother. She was the first Christian. She was the first to truly accept Christ and the first to evangelize. She was there at every stage of His life and ministry. She was present at His trial, his cruxificition, His death, His resurrection, the first Pentecost and His Ascension.
If those who personally knew and loved the risen Lord call her Theotokos, what credibility have those who disagree?