Because the Jewish festivals were shadows pointing forward to Christ's death on the cross and High Priestly intercession in heaven as per Col 2:14-16; Heb. 9:9,10. These have met their "substance" in Christ. The 10 Commandments are moral commands of conduct, that existed in heaven and currently exist in heaven (Revelation 11:19; 15:5). The Sabbath points "backward" to Creation week, as per Exodus 20:11. It was made "for" "mankind".
We have no allusion to the Seventh-Day Sabbath of the 4th commandment being a shadow anymore than we find the other 9 of not worshiping idols, not stealing, murdering, committing adultery, not coveting, etc. etc. being a shadow.
All the earthly ceremonial types finding their meaning spiritually in the New Covenant.
Here are some examples of how all the earthly ceremonial services meet their antitypical, and spiritual reality:
I beseech you therefore, brethren, by the mercies of God, that ye present your bodies a living sacrifice, holy, acceptable unto God, which is your reasonable service. (Romans 12:1)
Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin. (Romans 6:6)
"Ye also, as lively stones, are built up a spiritual house, an holy priesthood, to offer up spiritual sacrifices, acceptable to God by Jesus Christ. (1 Peter 2:5)
"It was therefore necessary that the patterns of things in the heavens should be purified with these; but the heavenly things themselves with better sacrifices than these." (Hebrews 9:23)
"And to love him with all the heart, and with all the understanding, and with all the soul, and with all the strength, and to love his neighbour as himself, is more than all whole burnt offerings and sacrifices." (Mark 12:33)
"By him therefore let us offer the sacrifice of praise to God continually, that is, the fruit of our lips giving thanks to his name.But to do good and to communicate forget not: for with such sacrifices God is well pleased." (Hebrews 13:15,16)
"And walk in love, as Christ also hath loved us, and hath given himself for us an offering and a sacrifice to God for a sweetsmelling savour." (Ephesians 2:5)
"But I have all, and abound: I am full, having received of Epaphroditus the things which were sent from you, an odour of a sweet smell, a sacrifice acceptable, wellpleasing to God." (Philippians 4:18 )
"And they that are Christ's have crucified the flesh with the affections and lusts." (Galatians 5:24)
"And ye are complete in him, which is the head of all principality and power: In whom also ye are circumcised with the circumcision made without hands, in putting off the body of the sins of the flesh by the circumcision of Christ." (Colossians 2:10,11)
"For he is not a Jew, which is one outwardly; neither is that circumcision, which is outward in the flesh: But he is a Jew, which is one inwardly; and circumcision is that of the heart, in the spirit, and not in the letter; whose praise is not of men, but of God." (Romans 2:28, 29)
"For we are the circumcision, which worship God in the spirit, and rejoice in Christ Jesus, and have no confidence in the flesh." (Philippians 3:3)
"Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth." (1 Cor 5:8 )
And concerning the sprinkling of blood we find:
"Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water." (Hebrews 10:22)
"And to Jesus the mediator of the new covenant, and to the blood of sprinkling, that speaketh better things than that of Abel." (Hebrews 12:24)