Because God wills it. He is the God who decided to make a physical creation, to form man with a physical body--before the fall into sin, which brought death and decay into the world--and to then send an incarnate ("in-the-flesh") Savior to redeem both soul and body and restore creation, and who himself rose from the dead and ascended into heaven bodily.
I’m aware of what the Bible says but am suggesting that that interpretation may have a spiritual meaning and not a literal one. Consider the body to the soul like the cage to the bird. The bird doesn’t need the cage to exist, and, in fact, would be happier without it.
What you have just stated, almost perfectly--and hopefully unintentionally--is the ancient Gnostic heresy, which the Bible rejects and the church condemns. The resurrection of the flesh, the resurrection of the body, is a biblical doctrine that is absolutely firm and certain and trustworthy.
Charles, I am aware of your theology and beliefs and I respect them. I simply offered the possibility of another interpretation beyond the literal. If I read of someone who ‘flew out the door’, I suppose a case could be made that they were claiming the ability to fly.