It's the same everywhere in the world. But just because he wasn't convicted and you don't like it doesn't make him guilty legally. It could have gone to trial and similar to OJ Simpson, be acquitted yet people would say there is this evidence that they cannot forget and therefore can't shake the feeling that he got away. Ultimately, the authorities in the UK dropped charges because they thought they couldn't convict him. It happens everyday in all type of crimes. All these people are not considered guilty by law. A lot of the issue here is due to that audio/video evidence that people saw, and now they think this is all of it.Maybe you don't how UK law works as I know it is different in the States. But the reason Greenwood was not convicted was not because he was found to be innocent or because he produced evidence to show that he did not commit the crimes he was charged with. It was because his partner withdrew her testimony. Remember this is the partner that he broke his bail conditions by approaching and spending time with, when he was not meant to be anywhere near her. Without her evidence, the Crown prosecution service (which prosecutes all crimes in the UK) decided they didn't have a realistic chance of proving his guilt beyond all reasonable doubt and so they dropped the charges. That in no way presumes innocence.
Like many have said, even if the victim became hostile, the authorities could have pressed charges. They had this famous audio/video evidence. If they chose not to despite this evidence that seems so certain that many are unwilling to change their stance, then it doesn't add up. It's either the evidence is so strong, and even if the victim testified against the prosection, he would get convicted, or somehow it's not strong enough and couldn't get a definite conviction as soon as the victim doesn't want to cooperate. Therefore, I think that we must be missing a whole picture.
And the reason why the family is not releasing anything? Whatever happened in the rest of the audio/video, while not related to domestic violence, must not be great. Therefore, they don't see any benefit of releasing it.