Why is everything created spiritually before physically?

According to LDS doctrine, why are we created as spirits before we can receive a body? On earth, all creatures are born with the same bodies as their parents. In the preexistence, why are the children of God born/created out of different matter (spirits) than our heavenly parents? Our Father in Heaven is a physical being. If we are literal offspring of our Father in Heaven, then why aren't we born in the pre-earth life with a physical body, the same as our Father in Heaven?