Basically for the same reasons we do not keep the law of Moses --we are under the new covenant- the law of Christ. It says the law came through Moses and grace and truth through Jesus Christ. John is showing the difference between the two covenants

First- The Sabbath was given to Israel not the world and it was done as a sealing of the covenant of law.

Exodus 31:16-17 “Therefore the children of Israel shall keep the Sabbath, to observe the Sabbath throughout their generations as a perpetual covenant. It is a sign between Me and the children of Israel forever; for in six days the LORD made the heavens and the earth, and on the seventh day He rested and was refreshed.”

Clearly the Bibles meaning of the children of Israel is the nation of Jews who were released from bondage in Egypt. Gentiles were not called Jews, or Israel unless they converted.

Ezekiel 20:12 emphasizes: Moreover also I gave them (Israel) my Sabbaths, to be a sign between me and them”

The Sabbath was made for man as a day of rest, not worship (the word Shabbat means to cease work) but it was not given to anyone until Moses time and then it was given to a nation all at once. There is no command or punishment for not keeping the Sabbath until Israel was released from Egypt. You do not see Adam, Enoch, Noah, nor Abraham (the first Jew) keeping the Sabbath. Sabbatarians are hard pressed to force their doctrine into the pages of sacred Scripture by retreating to the Genesis account where it only mentions God resting from the creation. He is the only one who worked, therefore he rested on the 7^th day, and did so only once (typifying the 7th day he gives the church that is rest in Christ Heb.4). Not even the book of Hebrews that is trying to encourage the Hebrew believers to mature corrects them on or has anything to say about the Sabbath day as required for the church.

The Jewish believers of the first century church were never commanded to teach the gentiles to obey this day. Acts 15:28-29: "For it seemed good to the Holy Spirit and to us to lay upon you no greater burden than: these essentials: that you abstain from things sacrificed to idols and from blood and from things strangled and from fornication; if you keep yourselves free from such things, you will do well." This is why in James 2 it says: “For whoever keeps the whole law and yet stumbles in one point, he has become guilty of all.”

It was the Jews that made an idol of the Sabbath and challenged Jesus with everything He did according to their own interpretation of the Sabbath and law. The Sabbatarians today are no different in the way they challenge the church making it a requirement when it is not.

Neither is there Scripture that teaches that the Sabbath has been transferred to another day, from Saturday to Sunday. The Sabbath is still from Sundown Friday night until sundown Saturday. Sunday is not the Sabbath.  New Testament believers met on the first day of the week because they celebrated the resurrection (Lk. 24; Jn. 20), Instead of  the Sabbath which was of the old covenant.  the Church did not hold the first day to be a holy day. There is no law or command to the Church to keep Sunday only. Sunday is not a day that replaced the Sabbath or the only day we are required to assemble and worship.

There are parts that are no longer binding because they were given to the Jewish nation. The whole of Moses law, except for a few moral portions were given for the first time to Israel, the Jewish nation, or were instituted from creation (such as marriage).

Rom.7 We are not under law but grace and it comes from being in Christ by the new covenant, not the old.

2 Cor 3:6-7 who also made us sufficient as ministers of the new covenant, not of the letter but of the Spirit; for the letter kills, but the Spirit gives life. But if the ministry of death, written and engraved on stones, - that is the law, to preach the law is to kill --to preach the gospel gives life.

The apostles preached Christ crucified. But to Sabbatrains it is always about the Sabbath.

the writer of Heb.8:7-8 For if that first covenant had been faultless, then no place would have been sought for a second. Vs.8 “Because finding fault with them, He says: "Behold, the days are coming, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah, he’s saying the first covenant is not perfect. V.13 In that He says, "A new covenant," He has made the first obsolete. Now what is becoming obsolete and growing old is ready to vanish away."

If the Sabbath is put aside then why are so many eager to revive it. Well they have listened to leaders who are unable to understand Scripture lead them from grace back into the bondage of the law. The commandment states in Exodus 34:21-23:"Six days you shall work, but on the seventh day you shall rest; in plowing time and in harvest you shall rest. "And you shall observe the Feast of Weeks, of the firstfruits of wheat harvest, and the Feast of Ingathering at the year's end. "Three times in the year all your men shall appear before the Lord, the LORD God of Israel.

Notice it says work 6 days of work not 5 then they are to have a shabbat rest, do you work 6 days or 5 like everyone else, If 5 then you are still breaking the law even though you may keep the Sabbath.

The Abolishment of the Law is declared by the Word of God: (2 Cor. 3:6-13; Eph 2:15); that Christ is the end of the law (Rom 10:4); that Jesus took away the first that He might establish the second, meaning they are not the same, nor a continuation (Heb. 10:5-9); and that now the righteousness of God is revealed without the law (Rom. 3:21-22). That we are no longer under the law, but under grace (Rom 6:14); that the Christian who seeks to keep the law to be justified or sanctified has fallen from grace of the new covenant (Gal 5:4).

Acts 2:42 states that the early Church followed not Old Testament laws but “the Apostles’ doctrine.”

The New Testament makes the observance of a particular day not a binding obligation but a choice. Romans 14:5-6 makes it clear that there was freedom in the matter of special days. Colossians 2:16-17 commanded the church not to allow anyone to act as their judge in regard to Sabbath days or feast days. And Galatians 4:9-10 warns against going back under the Law by insisting on observing by requirement the special days given to Israel. Those who make this mistake often hold to the church being a continuation of Israel or replacing her. If one wants to worship on Saturday or Sunday or any other day they have the freedom to do so under the new covenant of grace. It is when they make this a command- a requirement for all believers that they then break the command themselves to do so. Our biblical answer to Sabbatarians is that it was a sign only to the Jews, the nation of Israel not Christians just as the Bible teaches.