The answer lies in the fact that John though filled with the Spirit since the womb desired to be baptized of Jesus rather than baptize Him:
Matthew 3:13-15 Then cometh Jesus from Galilee to the Jordan unto John, to be baptized of him. (14) But John would have hindered him, saying, I have need to be baptized of thee, and comest thou to me? (15) But Jesus answering said unto him, Suffer it now: for thus it becometh us to fulfil all righteousness. Then he suffereth him.
Jesus was demonstrating to us that to fulfill all righteousness we must be baptized in water and the Holy Spirit:
John 1:33 And I knew him not: but he that sent me to baptize in water, he said unto me, Upon whomsoever thou shalt see the Spirit descending, and abiding upon him, the same is he that baptizeth in the Holy Spirit.
Acts 10:44-48 While Peter yet spake these words, the Holy Spirit fell on all them that heard the word. (45) And they of the circumcision that believed were amazed, as many as came with Peter, because that on the Gentiles also was poured out the gift of the Holy Spirit. (46) For they heard them speak with tongues, and magnify God. Then answered Peter, (47) Can any man forbid the water, that these should not be baptized, who have received the Holy Spirit as well as we? (48) And he commanded them to be baptized in the name of Jesus Christ. Then prayed they him to tarry certain days.
Most Christians are first born again as I was at 7 years old, then baptized in water some time later as I was in my 20s, then filled with the Holy Spirit years later such as I was at the age of 40. I know I was filled with the Spirit of Christ and led of the Spirit for those 33 years from 7 to 40:
Romans 8:9 But ye are not in the flesh but in the Spirit, if so be that the Spirit of God dwelleth in you. But if any man hath not the Spirit of Christ, he is none of his.
But I was not filled with the Holy Spirit that led me into my wilderness to be tempted and overcome the devil until I was 40 as Jesus was when He was thirty:
Matthew 3:16-4:1 And Jesus, when he was baptized, went up straightway from the water: and lo, the heavens were opened unto him, and he saw the Spirit of God descending as a dove, and coming upon him; (17) and lo, a voice out of the heavens, saying, This is my beloved Son, in whom I am well pleased. (4:1) Then was Jesus led up of the Spirit into the wilderness to be tempted of the devil.
Luke 3:21-23 Now it came to pass, when all the people were baptized, that, Jesus also having been baptized, and praying, the heaven was opened, (22) and the Holy Spirit descended in a bodily form, as a dove, upon him, and a voice came out of heaven, Thou art my beloved Son: in thee I am well pleased. (23) And Jesus himself, when he began to teach, was about thirty years of age,...