"And the MERCHANTS of the earth weep and mourn over her,
The MERCHANTS here represent the economic leadership of the world's economies, just as the KINGS (verse 9) are the leaders of the religious organizations in the nation(s). There may only be one nation by this time with the beast running everything. These MERCHANTS in the past have dealt with tariffs, regulations, disasters and such, so to have them weeping and mourning here indications that the global economy has COLLAPSED. Ironically, this global economy may have been the result of a previous collapse of the individual economies of the existing nations. The EARTH BEAST apparently is allowed to set up this global economy at that time (Revelation 13:17).
Symbolically, religious organizations have become so entwined with the global economy just to survive, they think, that they, too, see their income disappear. Their "weeping and mourning" may be even louder when they realize how faithless they were in God's providence (Matthew 6:24-33-34).
because no one buys their CARGOES any more;
This is another way of saying that the global economy has collapsed.
Spiritually, the CARGOES are people's lives who are turned to RIGHTEOUSNESS. By this time, religious organizations have become so program driven that all they know are fund-raisers to support the LUXURIOUS THINGS listed in the next two verses. They have forgotten or maybe never learned how to operate in God's economy - Matthew 25:31-46.
Having said this, the greatest challenge of the gathering of believers today is to extricate themselves ENTIRELY from Babylon (verse 4) and the global economy. They must become like the kingdom of heaven (Matthew 13:45-46). (It is no coincidence that the above references are from Matthew; he was the former tax-collector-turned-disciple - Matthew 9:9-13. Matthew was one of the "economists" among the disciples.)