That's not what free market means. In a free market (which this is an okayish example of) buyers and sellers are free to set their own terms, rather than having them externally imposed. So you are free to try and negotiate a lack of exclusivity, it's just that likely nobody will take you up on it.

SEC oversite and similar mechanisms, by comparison, is an external imposition on the market.

Ironically, what you seem be suggesting (exclusivity terms "not allowed") could only be enforced by regulation, therefore making the market less free.