I still trust code more that a third party. Any of these platforms could act against me for any number of reasons. 

From being in cahoots with the other party to simply steal my shit, all the way to being forced to give up the key by a criminal actor, like a government agency. Also, human arbitrators make subjective interpretations and I may still disagree with their opinion, and there's nothing I can do if they decide against me.

The output of a smart contract is neither interpretable nor capable of conspiring or of being pressured into acting in a bad way.