Many stereotypes of Islam are rooted in prescriptions not in the Quran but in the Hadiths. Many observant Jews see the Talmud as integral to their religion.
Why did it come to be that most Christian sects ignored apocryphal writings like the Gospel of Thomas or the Gospel of Marcion?
I wouldn't compare the Hadiths or Talmud to Christian apocrypha like the Gospels of Thomas or Marcion. Instead I would suggest that they should be viewed as the equivalent of the writings of the Church Fathers, such as Clement.
The Gospel of Marcion isn't trying to add to the canon of Christian scripture or explain it. It is trying to replace parts of it. It isn't the equivalent to a Hadith. It is an equivalent to an alternative Koran.
The vast majority of canon law comes not from the bible itself but from what you would (incorrectly) call apocrypha - the writings of the church fathers in the couple of centuries after the death of Christ. Christianity absolutely uses sources outside of the bible and has had a tradition of doing so almost from the very beginning.