This is what torpedoed the first AI Assistant push in the late 1990's and early 2000s (see electric elves as an example). Basically we thought that personal travel assistants and open trading platforms would be cool things, but then discovered that content aggregators a) had a business model and b) could offer vertical integration and bulk buys, & discounts to goods providers and consumers, while also policing the platform. So we got Expedia and Ebay.

There is a more fundamental problem as well. Multi-agent systems require the programmer of the agent to influence the state of the agent in order that the agent can act to influence the states of other agents in the system. This is a very hard programming task.