Are they not a "legal fiction" in the way that a marriage, or a state, is legal fiction? Even in the absence of legislation codifying them they will still exist

Are they not a "legal fiction" in the way that a marriage, or a state, is legal fiction? Even in the absence of legislation codifying them they will still exist in some form. People will still form long term romantic relationships for the purpose of raising kids, joint decision-making, and ensuring that the other receives your possessions in death. Groups of people who share a language, culture, and geography will still form tribes or clans or some other form of institution even if it isn't strictly Westphalian statehood. Similarly, skilled workers will still find that their labor is more efficient when they work together. And with scale comes the need for sales, administration, and all the other components which make up a company as we know it today. I assume by "we" lacking imagination you mean humanity as a whole, and that just isn't true - we have lots of imaginative people who have attempted lots of different ways to arrange an economy, with varying degrees of success. We've tried flavors of state-run enterprise (from "crown corporations" here in Canada all the way to full collectivization in leftist and fascism in rightist systems) plus voluntary co-ops like kibbutz or communes. Not to mention publicly traded vs privately held corporations. Humanity has the imagination and often has had the pleasure of "experimenting" with various methods.