It STILL isn't in the constitution.
Your point?
And it's not commerce either. Thus it's a matter for the several states. It would be interesting to know how many State Constitutions give their governments power over marriage, and how many did so at the time the federal Constitution was written. It used to be a privat/religious matter. The states didn't get involved, directly that is. At the time the Constitution was written, not even the states required a "license" to marry.
Laws did reflect marriage however, but it need not be a religious marriage, it could be a "common law" marriage. Inheritance laws for example would reflect the marriage status of the deceased. Births were not recorded by the states either at that time.
In which case it's an issue for the States and the Federal Defense of Marriage is unconstitutional. The question is, would a gay marriage in one state (where it is legal) have to be recognized in another State under the Full Faith and Credit clause of the Constitution and to what extent can congress regulate the same pursuant thereto.