Earlier quoted context omitted.
Because the entities that control the machines and give their products away will be outcompeted by entities that keep the products to fuel their own growth. Over time, the former kind of entities will die out. This is a general argument, the "entities" could be rich people, companies, governments, AIs, etc.
Some of those general "entities" you speak of are composed of smaller entities. Trade (e.g. of labor) will occur between those smaller entities. Where there exists scarcity and a differential in value, trade will occur. Now, of course, that says nothing about the people that have nothing of value to trade with. But I'd argue that everyone has something to trade, it just might be of very low relative value. Even in su…
You can have something of value, but still be unable to find a trading partner, if that thing can be had for a cheaper price somewhere else. For example, if machines make labor cost less than a living wage, then you can't survive by selling labor.