Because Christ's atonement can only be applied to those the He chooses. It's not a free ticket. Christ took the debt on Himself. It is up to Him to decide to forgive our debt or not.
Do you somehow think that Christ doesn't obey the laws of the Celestial Kingdom and the Doctrine and Covenants? He doesn't have to make a decision to forgive. According to the Doctrine and Covenants, He has to forgive based on the law pertaining to forgiveness.
"I, the Lord, am bound when ye do what I say; but when ye do not what I say, ye have no promise." (Doctrine and Covenants 82:10)
"Nevertheless, he that repents and does the commandments of the Lord shall be forgiven;" (Doctrine and Covenants 1:32)
"In order to bestow His blessings on His children in a just and equitable manner, the Lord has instituted laws that govern those blessings that He wants all of us to enjoy. He has revealed this principle of laws to His prophet of the Restoration: 'There is a law, irrevocably decreed in heaven before the foundations of this world, upon which all blessings are predicated—and when we obtain any blessing from God, it is by obedience to that law upon which it is predicated.' ”
Daniel L. Johnson, “The Law of Tithing,”
Ensign, Nov 2006, 35–36
As for a free ticket, I don't know what you are talking about. However, I do know what God has told us about His free gift.
"But not as the offence, so also is the free gift. For if through the offence of one many be dead, much more the grace of God, and the gift by grace, which is by one man, Jesus Christ, hath abounded unto many." (Romans 5:15)
"For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord." (Romans 6:23)