Surrogacy contract. What if DNA test shows Surrogate and her partner are bio parents, not intended parents?

Isn't it a no brainer IF baby's DNA shows he/she matches biological mom (surrogate) and her partner DNA and not that of the intended parents that the baby will go home with his/her bio parents?  Makes sense to me, but am wondering why the intended parents, in a certain situation that I am aware of, seem to think this unborn baby will be theirs to take home from the hospital.  Isn't the fact that this baby is not biologically connected to the intended parents make the contract null and void?  Just curious.  :)