Because we're supposed to keep the commandments.
Love is a brief way to say it. However doing the commands defines the love. Its not arbitrary love of mans design in some loose sense.
Christians today are not taught The Bible in full. They're taught along subjective doctrinal lines.
Because of that; many don't know the difference between ordinance ,statutes, judgments, civil ,spiritual laws and so.
Currently people dont seem to know the old covenant did not take with it Gods laws or words.
It was only the blood rituals to forgive sins that were gone.
Colossians 2:14 “Blotting out the handwriting of ordinances that was
against us, which was contrary to us, and took it out of the way,
nailing it to his cross;”
G1378 δόγμα dogma dog'-mah From the base of G1380; a law (civil,
ceremonial or ecclesiastical): - decree, ordinance.
Jesus taught Gods laws:
Revelation 22:14 Blessed are they that do his commandments, that they
may have right to the tree of life, and may enter in through the gates
into the city.
Revelation 14:12 Here is the patience of the saints: here are they
that keep the commandments of God, and the faith of Jesus.
17 And the dragon was wroth with the woman, and went to make war with
the remnant of her seed, which keep the commandments of God, and have
the testimony of Jesus Christ.
Romans 3:31 Do we then make void the law through faith? God forbid:
yea, we establish the law.
17 And when he was gone forth into the way, there came one running,
and kneeled to him, and asked him, Good Master, what shall I do that I
may inherit eternal life?
18 And Jesus said unto him, Why callest thou me good? there is none
good but one, that is, God.
19 Thou knowest the commandments, Do not commit adultery, Do not kill,
Do not steal, Do not bear false witness, Defraud not, Honour thy
father and mother.
20 And he answered and said unto him, Master, all these
have I observed from my youth.
21 Then Jesus beholding him loved him, and said unto him,
One thing thou lackest: go thy way, sell whatsoever thou hast, and
give to the poor, and thou shalt have treasure in heaven: and come,
take up the cross, and follow me.
22 And he was sad at that saying, and went away grieved: for he had
(Likely ill gotten gains)
23 And Jesus looked round about, and saith unto his disciples, How
hardly shall they that have riches enter into the kingdom of God!
How can one call themselves Christian at the same time belittling Gods law ? Specially in His Commandments. That is His Word.