You want to know why? Because it's not there! It's silent on the matter except and unless the persons referred to in the 5th and 14th Amendments include unborn babies in which case, they would have the same Constitutional protections as you. They may be protected Constituionally but they sure as hell are not condemned by same.
But please, be my guest. Explain to me the Constitutional basis for the federal government making legal the taking of human life.
Very simple! Dred Scott v. Sanford (1857)