Sometimes because previous convictions of the accused could lead to 'an unfair trial'
In the case highlighted in the OP, it was obvious from the link that the accused had form for violent behaviour due to a previous case being highlighted in the press months previously. No one in the area he lived then would have been immune to the accused's past conviction. I do note however that the case was tried in a different area.
The next part of my post is somewhat off topic. But I feel it's important to the OP and the rough sex defence now being used in many cases.
All I'm going to say is that there is nearly always a background of violent behaviour when a murder takes place - I'm disregarding defence killings which strangely was the defence for the accused in the OP's post which the jury accepted (clearly, this is suspect given his now known past violent behaviour).
There are many women who disappear, presumed dead, and their bodies are never found. A prime example is the case of Ted Bundy whose known victims (30) are now presumed to be, sadly, the tip of the iceberg when it comes to how many he actually killed.
Murdering people by physical force using hands or a hand held weapon is the hallmark of a serial killer and there is always a sexual element to it.