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?
Technically, we are not first created as spirits. This is a simplification. We existed as intelligences, which are not clearly explained, and later formed into our spirits by God.

Man was also in the beginning with God. Intelligence, or the light of
truth, was not created or made, neither indeed can be. D&amp;C 93:29

Speaking of this topic, Marion G. Romney has said:

In origin, man is a son of God. The spirits of men “are begotten sons
and daughters unto God” (D&amp;C 76:24). Through that birth process,
self-existing intelligence was organized into individual spirit
beings.

After that physical form was created to house the spirits.

Our bodies, my brethren, our minds, are the tabernacles of our
spirits. - Gordon B. Hinkcley

By extension, it is reasonable to believe that all life also came from intelligences, which may not have been suited to become human. Therefore things are created or organized spiritually first, because without the spiritual existence there is no purpose in the physical creation.
For further reading, I recommend the article on Intelligences in the Encyclopedia of Mormonism