Who says they're not?
Jesus came to fulfil the law and the prophets.
He fulfilled the sacrificial law when he offered his life - the life of the spotless Lamb of God - for our sin.
He fulfilled the prophets who spoke of his coming, his teaching, his healing ministry, his entry into Jerusalem, his suffering, etc, and that he would establish a NEW Covenant.
Jesus also spoke of the 10 commandments, and summarised them in two; love God with all your heart, mind and strength and love your neighbour as yourself. As well as this, he also gave us a NEW commandment; to love others as HE loved us. How did he love us? He died for sinners - laid down his life for people who hated him, had sinned against his Father and did not deserve anything from God, except eternal death.
That is how we should love others. And obviously, if we are, we will not kill or injure them, take their wives or their property, covet their possessions and so on.
Everything that Jesus told us to do is covered in the 10 commandments; love God, seek first his kingdom, decide whether to serve God or money, come to Jesus to receive rest, and his peace, and treat, love and forgive people as we want them, and God, to treat, love and forgive us. Jesus also taught much more than is in the commandments, because they don't tell us how to be saved.
But loving our neighbour means that we don't kill him; so we are keeping the commandments.