If a particular species is useful for some concrete purpose, then someone with deep enough pockets can easily be found who will invest into breeding it for profit. If not, who cares?

Me. And I'm not alone. Many humans do value the preservation of significant elements of biodeversity that don't have any 'concrete', objective value. This is arbitrary only in the sense that any terminal value is arbitrary. I suggest that it is not nearly as 'easy' to find someone to preserve a given part of the commons, even when that part would be considered value by the extrapolated volition of the population.