Seven Feasts? Looks like six according to the holy scriptures, seven if you include the weekly sabbath, and eight if you include the feast of Lights.
Christians do not keep them because they are not commanded to keep them by God. The feasts were given to Israel under the old covenant. Since that covenant is abrogated now and the new covenant in Christ is in effect Christians keep the one feast commanded under the new covenant - specifically the holy supper of the Lord Jesus Christ.
Speaking of the new covenant in contrast with the old covenant saint Paul writes: God has made us suitable ministers of the New Testament, not in the letter, but in the Spirit. For the letter kills, but the Spirit gives life. But if the ministration of death, engraved with letters upon stones, was in glory, (so much so that the sons of Israel were not able to gaze intently upon the face of Moses, because of the glory of his countenance) even though this ministration was ineffective, how could the ministration of the Spirit not be in greater glory? For if the ministration of condemnation is with glory, so much more is the ministration of justice abundant in glory. And neither was it glorified by means of an excellent glory, though it was made illustrious in its own way. For if even what was temporary has its glory, then what is lasting has an even greater glory. (2 Corinthians 3:6-11) He says of the old covenant that it was engraved with letters upon stone and that it is a ministration of death and the ministration of condemnation but of the new covenant he says it is the ministration of the Spirit that is of far greater glory than the old covenant.
The author of the book called Hebrews writes: We have so great a High Priest, who is seated at the right hand of the throne of Majesty in the heavens, who is the minister of holy things, and of the true tabernacle, which was established by the Lord, not by man. For every high priest is appointed to offer gifts and sacrifices. Therefore, it is necessary for him also to have something to offer. And so, if he were upon the earth, he would not be a priest, since there would be others to offer gifts according to the law, gifts which serve as mere examples and shadows of the heavenly things. And so it was answered to Moses, when he was about to complete the tabernacle: "See to it," he said, "that you make everything according to the example which was revealed to you on the mountain." But now he has been granted a better ministry, so much so that he is also the Mediator of a better covenant, which has been confirmed by better promises. For if the former one had been entirely without fault, then a place certainly would not have been sought for a subsequent one. For, finding fault with them, he says: "Behold, the days shall arrive, says the Lord, when I will consummate a New covenant over the house of Israel and the house of Judah, not according to the covenant which I made with their fathers, on the day when I took them by the hand, so that I might lead them away from the land of Egypt. For they did not remain in my covenant, and so I disregarded them, says the Lord. For this is the covenant which I will set before the house of Israel, after those days, says the Lord. I will instil my laws in their minds, and I will inscribe my laws on their hearts. And so, I will be their God, and they shall be my people. And they will not teach, each one his neighbour, and each one his brother, saying: "Know the Lord." For all shall know me, from the least, even to the greatest of them. For I will forgive their iniquities, and I will no longer remember their sins." Now in saying something new, he has made the former old. But that which decays and grows old is close to passing away. (Hebrews 8:1-13) The holy scripture quoted above says that God has made the former covenant old and that which decays and grows old is close to passing away. Christians live according to new covenant which was confirmed with better promises. But you may ask how can the old covenant be eternal while at the same time be abrogated? The answer is given in saint Paul's letter to the Romans where he reflects upon the meaning of baptism and on the teaching of Christ.
So what shall we say? Should we remain in sin, so that grace may abound? Let it not be so! For how can we who have died to sin still live in sin? Do you not know that those of us who have been baptised in Christ Jesus have been baptised into his death? For through baptism we have been buried with him into death, so that, in the manner that Christ rose from the dead, by the glory of the Father, so may we also walk in the newness of life. For if we have been planted together, in the likeness of his death, so shall we also be, in the likeness of his resurrection. For we know this: that our former selves have been crucified together with him, so that the body which is of sin may be destroyed, and moreover, so that we may no longer serve sin. For he who has died has been justified from sin. Now if we have died with Christ, we believe that we shall also live together with Christ. For we know that Christ, in rising up from the dead, can no longer die: death no longer has dominion over him. For in as much as he died for sin, he died once. But in as much as he lives, he lives for God. And so, you should consider yourselves to be certainly dead to sin, and to be living for God in Christ Jesus our Lord. (Romans 6:1-11) Saint Paul teaches that Christians are dead as far as the provisions of the Laws given to Moses are concerned. Consequently Christians are alive in Christ yet dead to the provisions of the old covenant having been buried with Christ in baptism and having risen with Christ. Thus Christians are both living in accord with the law because they are alive in Christ who obeyed the law and all of its commandments. So, while Christians are dead to sins because they died with Christ they are also alive in Christ and live according to the new covenant sealed in his blood. Thus Christians are under obligation only to their Lord and not to the laws given by God to Moses.
I hope this also helps with bill's questions.