One of the functions of colonialism (in this case colonialism via exploitation of labor and resources of the global south economically) is to transfer wealth from the colony to the empire (we call these the Imperial Core regions).

I'm going to use a really simplified example and some made up numbers to illustrate. Say a pound of coffee takes 1 hour of labor to produce. The people producing it in Ethiopia are being paid $1 an hour to produce it. A capitalist from the Imperial Core buys that pound of coffee for $2, ships it to the Core for another $1, and sells it for $5.

The capitalist makes $2 and the buyer gets a pound of coffee for $5. Now imagine if the worker in Ethiopia is being paid $12 an hour. The capitalist cannot buy a pound of coffee for anything less than $12. After $1 shipping and his $2 cut (assuming he does not inflate his cut because he's taking a percentage of the sale), the pound of coffee is now $15 to the buyer.

The buyer does not have the Ethiopian worker "working for them" in the strictest sense, but the buyer does benefit from getting their pound of coffee for 1/3 the price they would otherwise have to pay.

This is why Marxists say that the current living standards of the so-called First World are being propped up by the economic exploitation of the global south, even if the residents of the First World are not directly engaging in colonialism in the pith helmet and whips sense.