I understand that companies want to avoid getting into legal complications over it, and that's why I think there should be some sort of legislation in place to force companies to explain decisions like this. This is becoming more and more important with time.
Something like: If you end your contract with someone because you think that they were in violation of the terms, you have to clearly list what your reasoning is for it, with no tolerance for black box answers.
DMCA takedown requests include the list of offending URLs. This should be made similar. "We terminated our contract because this, this, and this signal, make us think that you're in violation of its terms". You can then appeal, and obviously if the two parties can't come to an agreement by themselves, you can at least use the legal system.
Otherwise, we're living in a world where contracts between two parties mean nothing. Anyone can pull out of anything at any time for any reason, with no notice.