The real question you should be asking is why the Bible doesn't answer that itself.
The biggest problem of the Bible is that its books are written as historical accounts of events by people recounting stories passed down from many years earlier (the historical books passed down orally hundreds of years before Christ) to 50-100 years after Jesus' death. And while recounting events and happenings, give little or no insights into the causes and reasons.
My answer to this is that Jesus Christ and his church were never meant to simply be the writings of a book only. The true church of Jesus Christ was always meant to have continuing revelation where such question could be asked and answered through revelation. Shortly after many of the Apostles of Jesus were murdered, the true church of Jesus gradually fell into a state of apostasy and needed to be restored to the earth again. In 1830 the Lord restored his true church once again upon the earth and it is known as The Church of Jesus Christ of Latter-day Saints. In the church today through the revelations of God, we understand that God our eternal Father in Heaven is a being who like Jesus has an immortal body of flesh and bones. Receiving a body in this life is part of the eternal plan of God and that having a body brings to our spirits eternal joy and happiness. This was revealed in a revelation to the prophet Joseph Smith:
Doctrine and Covenants 93:33-34
33 For man is spirit. The elements are eternal, and spirit and element, inseparably connected, receive a fulness of joy;
34 And when separated, man cannot receive a fulness of joy.
For this reason God has given us all bodies and eventually our bodies will die and resurrect to be immortal and we will have them for ever and ever and be able to receive a fulness of joy.
Matthew 16:13-18
13 When Jesus came into the coasts of Cæsarea Philippi, he asked his disciples, saying, Whom do men say that I the Son of man am?
14 And they said, Some say that thou art John the Baptist: some, Elias; and others, Jeremias, or one of the prophets.
15 He saith unto them, But whom say ye that I am?
16 And Simon Peter answered and said, Thou art the Christ, the Son of the living God.
17 And Jesus answered and said unto him, Blessed art thou, Simon Bar-jona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven.
18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it.
In the above verse, Jesus asks his disciples, "Whom do men say that I the Son of man am?" To this some of the disciples list John the Baptist, Elias, Jeremias or one the ancient prophets. But Jesus then asks them personally, "Whom say ye that I am?" To this Peter answers and says, "Thou art the Christ, the Son of the living God." Jesus then tells Peter, "Blessed art thou, Simon Bar-jona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven. This knowledge was not given unto Peter by mankind but by God the Eternal Father which is in heaven. It was given to him by revelation. Peter took the time to pray and learn by revelation that Jesus was the very Christ, the son of the living God. Jesus then tells Peter, "thou art Peter, and upon this rock (the rock of revelation) I will build my church; and the gates of hell shall not prevail against it.
Revelation was to continue in the church. The gates of hell cannot stand against a church which receives continuing revelation from God himself. The people in a church can fall away from truth and apostatize from it, but a faithful church whose people hold to the truth and continue to receive revelation from God cannot fail. Shortly after the days of the apostles of Christ, the church began to fall away into apostasy and many great truths of the gospel of Jesus Christ were lost. But God would not allow Satan to prevail over him and restored his church again upon the face of the earth. Today, through the revelations of God, we understand the importance of the resurrection and why it is so critical that Jesus resurrect and become just like his Father and why it is so important for all mankind to have a body and also eventually resurrect for all eternity.