Because Jesus is NOT like an OT sacrifice that had to be offered for sin like the animal.
Jesus gave Himself for us. He laid down His own life.
He did not come to give Himself to us to be used by us so we cold present Him to God on our behalf every time we sinned.
Catholics miss the part about just how much a person sins every day. They are so focused on the outward and external acts just like any works based religion, but God focuses on the heart.
King David, for all his murder and adultery, was still considered a man after God's own heart. The pharisees had the Law down perfectly and could keep it to a *T*, but Jesus had pretty harsh words for them.
Paul had this to say about his works........
Philippians 3:2-15 Look out for the dogs, look out for the evildoers, look out for those who mutilate the flesh. For we are the circumcision, who worship by the Spirit of God and glory in Christ Jesus and put no confidence in the flesh— though I myself have reason for confidence in the flesh also. If anyone else thinks he has reason for confidence in the flesh, I have more: circumcised on the eighth day, of the people of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; as to the law, a Pharisee; as to zeal, a persecutor of the church; as to righteousness under the law, blameless. But whatever gain I had, I counted as loss for the sake of Christ. Indeed, I count everything as loss because of the surpassing worth of knowing Christ Jesus my Lord.
For his sake I have suffered the loss of all things and count them as rubbish, in order that I may gain Christ and be found in him, not having a righteousness of my own that comes from the law, but that which comes through faith in Christ, the righteousness from God that depends on faith— that I may know him and the power of his resurrection, and may share his sufferings, becoming like him in his death, that by any means possible I may attain the resurrection from the dead. Not that I have already obtained this or am already perfect, but I press on to make it my own, because Christ Jesus has made me his own. Brothers, I do not consider that I have made it my own. But one thing I do: forgetting what lies behind and straining forward to what lies ahead, I press on toward the goal for the prize of the upward call of God in Christ Jesus.
For All Catholics depend on them and brag on them, Jesus had this to say also.
Luke 18:9-14 He also told this parable to some who trusted in themselves that they were righteous, and treated others with contempt: “Two men went up into the temple to pray, one a Pharisee and the other a tax collector. The Pharisee, standing by himself, prayed thus: ‘God, I thank you that I am not like other men, extortioners, unjust, adulterers, or even like this tax collector. I fast twice a week; I give tithes of all that I get.’
But the tax collector, standing far off, would not even lift up his eyes to heaven, but beat his breast, saying, ‘God, be merciful to me, a sinner!’ I tell you, this man went down to his house justified, rather than the other. For everyone who exalts himself will be humbled, but the one who humbles himself will be exalted.”
Matthew 7:21-23 “Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven. On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’ And then will I declare to them, ‘I never knew you; depart from me, you workers of lawlessness.’
Jesus never denied that mighty works were done.