Just because something is achieved contractually does not mean it doesn't undermine market mechanisms. Cartels are contractual but that still undermines the market.

There is a proposition in the law of property that restraints on the alienation of land are to be avoided whenever possible. restrictions on alienation reduce the fungibility of property and increase transaction costs, reducing efficiency. In some states, e.g. NY, there are limits on what sorts of restrictions on alienation courts will enforce when written into deeds.