Pretending that nothing happened would have shattered his authority.
In the play Antigone is seen by the common folks as a woman of exceptional kindness and bravery who risks her own life to fulfill her family duty and just a duty of a human – releasing the soul of her brother for the afterlife.
Not allowing to bury the dead body was, in ancient Greek culture, the crime much more brutal than the murder itself: instead of ending the mortal life of a person the offender banished them from afterlife for all the eternity.
If Antigone yielded to her King, she would be pardoned.
But she fiercely decided to take her own life, just not to give him the pleasure, not knowing that King Creon changed his mind and was riding to spare her life and bury Polyneices instead.
Hearing the refusal of Creon to bury Polyneices, she doesn’t resort to convincing and doesn’t remind him of traditions and mercy.
Instead she just disobeys her King, questioning his authority and showing that she can go against his will without any repercussions.
Creon doesn’t have the single fatal flaw that the true tragic hero must fall a victim of.
Though he looks like a hostage of his position – he can’t let Antigone go with what she has done, because it questions his political power and his position as a King.
Story-wise, Antigone deserves all the compassion the locals give to her.
Even her bravery bordering with recklessness and her desire to die on her own terms are portrayed as something worth respect. Maybe, the townspeople don’t see the need of it: he looks like an authority free to do whatever he pleases.