That may have been true while the case was ongoing but the major problem is that the story isn't gripping because everyone knows the ending and there are no loose ends or unsolved details that raise more questions.
If the stalkers are still alive or even jailed, there is still an inherent sense of the unknown which is what drives people to consume media. And also (thankfully), neither of the two suffered any sort of physical harm aside from having a petrol bomb thrown at their driveway. That alone isn't shocking enough to sell a book.
This is the reason survivors of terrorism rarely manage to write sellable books either, particularly those who remained uninjured. Writing a book about "I was very scared when this scary thing was happening" does not convey any real emotions to a reader if we already know the source of the threat is dead. This is compounded if the crime was obscure enough that it's not a universal threat, such as a really bizarre form of stalking or an isolated act of terror.
Things like abuse, addiction, illness or relationship stalking are sellable because they are universal topics that could happen to anyone. People don't relate to getting scammed by a mentally ill neighbour because the majority may feel they would have made different decisions along the way.
It seems like a poor editorial decision to pick up such a story, especially with an extremely AI-sounding style of prose. The couple have no doubt suffered a lot however the way the story was conveyed to the public is simply not marketable as a product.