If we imagine a Jeffersonian world of yeoman farmers, then most commercial interactions would be of this voluntary kind. If the farmers are largely self-sufficient, and there exist enough variety of sources for those necessities which they cannot themselves produce, then it would be fair to say that their commercial actions are voluntary. They need metal tools, but there exists such competition as to prevent monopolies or cartels. They want tea, but that's a luxury. In this world, a logic of market-based voluntarism may work.
But, that isn't our world. In our world, most people own very little or no economically productive property, while a few people own a very large amount of productive property. For the dispossessed majority to survive, they have to self themselves into the service of the possessed minority. The alternative is starvation, or at least, assuming a baseline of welfare or charity extended even to those who are unwilling to work, intense poverty. That does not appear to be very much of a choice, so it seems difficult to regard this as a wholly voluntary choice. Perhaps a degree of free reign is retained, in that the dispossessed might be able to choose between employers, or set some conditions of employment, especially in times when their labour is in relative demand. But the basic compulsion to work, to seek employment, to sell oneself into servitude, remains. It is not a free choice. It is not voluntary.