Ephesians 5:1 is not the beginning of a topic. The entire letter flows with instructions aimed at increasing unity in the church community at Ephesus.
The subject matter in question also began in the previous chapter. After uniting the 'uncircumcised' and 'the circumcised' as one citizenship in Christ (Ephesians 2: 11-22), Paul then charges the people to work on becoming united as one body in Christ:
Be completely humble and gentle; be patient, bearing with one another in love. Make every effort to keep the unity of the Spirit through the bond of peace. (Ephesians 4: 2-3)
Paul concentrates on two ways they should do this. From 5:21 to 6:9 Paul explores relationships with uneven power distribution (husband/wife, parent/child, master/slave). Here he calls for humility and forbearance from the powerless, loving care from those in authority, before urging them all to unite in the battle for Christ.
But before this, Paul firstly calls on the Ephesians to distance themselves from their old way of living - to put off their old self and put on the new self:
So I tell you this, and insist on it in the Lord, that you must no longer live as the Gentiles do, in the futility of their thinking. They are darkened in their understanding and separated from the life of God because of the ignorance that is in them due to the hardening of their hearts. Having lost all sensitivity, they have given themselves over to sensuality so as to indulge in every kind of impurity, and they are full of greed.
That, however, is not the way of life you learned when you heard about Christ and were taught in him in accordance with the truth that is in Jesus. You were taught, with regard to your former way of life, to put off your old self, which is being corrupted by its deceitful desires; to be made new in the attitude of your minds; and to put on the new self, created to be like God in true righteousness and holiness. (Ephesians 4: 17-24)
Paul then contrasts this old and new self from 4:25 through to 5:20, specifically in words and deeds - how we relate to others. He contrasts falsehood with speaking truthfully, and anger with love, expanding this out to look specifically at the 'old' tendencies to 'sin' in anger, but also to 'sin' in love.
In Ephesians 4:28-32, Paul contrasts the 'old' behaviour and talk in relating to those who provoke our anger with more loving options.
"In your anger do not sin”: Do not let the sun go down while you are still angry, and do not give the devil a foothold. Anyone who has been stealing must steal no longer, but must work, doing something useful with their own hands, that they may have something to share with those in need.
Do not let any unwholesome talk come out of your mouths, but only what is helpful for building others up according to their needs, that it may benefit those who listen. And do not grieve the Holy Spirit of God, with whom you were sealed for the day of redemption. Get rid of all bitterness, rage and anger, brawling and slander, along with every form of malice. Be kind and compassionate to one another, forgiving each other, just as in Christ God forgave you.
In Ephesians 5:1-7, he warns against the 'old' behaviour and talk in relating to those we love that is not in fact loving. He also suggests that we disassociate with those who behave (5) or speak (6) in this way, because they invite God's wrath (7).
Follow God’s example, therefore, as dearly loved children and walk in the way of love, just as Christ loved us and gave himself up for us as a fragrant offering and sacrifice to God.
But among you there must not be even a hint of sexual immorality, or of any kind of impurity, or of greed, because these are improper for God’s holy people. Nor should there be obscenity, foolish talk or coarse joking, which are out of place, but rather thanksgiving. For of this you can be sure: No immoral, impure or greedy person—such a person is an idolater—has any inheritance in the kingdom of Christ and of God. Let no one deceive you with empty words, for because of such things God’s wrath comes on those who are disobedient. Therefore do not be partners with them.
Paul then rounds out this section by returning to the image of darkness from 4:18, contrasting the old 'fruitless deeds' with the 'fruit of light', and the foolishness of getting 'drunk on wine, which leads to debauchery' with being 'filled with the Spirit', which leads to making music and singing songs to the Lord.
The beginning of Ephesians 5 is part way through Paul's efforts to contrast the old self of the Gentiles with the new self as 'created to be like God in true righteousness and holiness', one of two main ways he suggests to enhance the unity of the church community in Ephesus. By portraying the community as united against outside forces - namely the old ways of the Gentiles and 'against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realms' (Ephesians 6:11) - he attempts to steer the focus away from their various internal conflicts.
After contrasting the Gentiles' behaviour and talk with more loving options in situations of anger, Paul then categorised ways that the Gentiles also corrupted their love for each other: in their actions with sexual immorality, impurity and greed, and in their words with obscenity, foolish talk or coarse joking. He warns that this is not how to 'walk in the way of love'.
As for the question of 'primary reasons', these are not reasons, but categories of 'deceitful desires' in supposedly 'loving' relationships. Greed, for instance, would likely include possessiveness, jealousy, polygamy, rape, etc.