Their patent sharing terms say that they get rights beyond patents or copyright: if you use their patents you agree not to copy any of their "designs," a vague term that no one can really be sure of how expansive it is.
You misunderstand: (at least some of) Tesla's patents are likely enforcable. It's the terms under which they can be used in the "patent sharing agreement" which are vague and quite expansive (which is quite possible to enforce in contract/licensing law, and the courts are willing to take very extreme positions on in business to business cases), and that is why no-one has engaged with it.