Romans 5:12 Wherefore, as by one man (Adam) sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned.
Because Adam's bloodline was the beginning of all men, and "death passed upon all men"
Remember, we don't die for Adam's sin, but we die because of Adam's sin.
We may lose our body to death, but we do not have to lose our soul to it.
God so loved the world, that He gave His only begotten Son, that whosoever believes in Him should not perish (or experience eternal death).
Born again believers are free indeed from eternal death, but they are still subject to natural death through the judgment of the bloodline curse of Adam.
Physical Death is precious for a believer in the sight of God because it is like unto a bride heading to her husband.
Psalm 116:15