Because that soul and body formed a person who was more holy than most, and thus sanctified his (or in this case, her) body, which is thereby preserved from the corruption which normally afflicts corpses in a fallen world.
In Orthodox thought, bodies and souls are of equal importance (rather than the Gnostic idea of the living soul animating an essentially dead body). An Orthodox thinker would say that we are our bodies (unlike many Western Christians), but not just our bodies (unlike a materialist).
Sure it does.
> Why would the body be preserved without the soul?
As a sign of God's power, as a message to others, the same as any other miracle.
Well sure, but you might as well point out the stain in the corner is a "sign of God's power". It seems to me the "correct" approach would be to appreciate the ineffability of what happened, not make ridiculous claims about holiness causing preservation when there is literally no rational implication of this.