It’s a good question, but you’re contracted to do a certain amount of promotion by your publishers’ publicity dept, so some publicity was inevitable. When she signed a book contract she committed to that, we can’t know with how much trepidation.
Then, I imagine, when it became a bestseller, everything snowballed. Maybe at first it was hard to then say ‘No, I suddenly no longer want to promote my book despite getting awards and invitations to literary festivals and tv interviews’, and then maybe, as (presumably) no one had bobbed up in the front row at Haye to ask awkward questions about the court case or Moth’s continuing health, she thought they were safe, and the past was the past. Maybe they started to believe their own cover story and relax. No one had come out of the woodwork.
It did, after all, take a very long time for someone to contact a journalist with their doubts about the Walkers’ credibility. TSP came out in 2018, and two further books had appeared to further high sales, and a film was optioned and made before CH got in contact with her questions. Then they knew it was only a matter of time before the story broke, and had time to disappear from public view without any pressing need to emerge again, cushioned by money.
And, apart from that quickly-deleted statement from the nephew, no one from their circle has spilled any beans. No damning information has come from siblings, children, friends, Dave and Julie etc etc. Loyal and discreet, betrayed and shocked but unwilling to talk, paid off, implicated, feeling like idiots and not wanting to put themselves out there etc etc?