Elemental natures can interfere with bindings, yes; it's discussed the Roll of Glorious Divinity.  It comes down to, Heaven and the Exalted were on the same side; the Exalted and Malfeas were not.  So when the time came to make the deals that were made, Heaven got something equitable, and Hell got the 'and if you don't agree to our terms, we'll kill you' deal.