Bob Woodward's decision to withhold audio tapes of Trump admitting he was lying about COVID was unethical, the latest example of a now-common practice used to sell books. People like John Bolton and Michael Cohen have to save some "surprise revelations" to keep people interested enough to pay for the book when the release date arrives. In that sense, the publishing industry as well as the individual authors bear some responsibility here.
An overlooked factor, though, is how little newspaper reporting of the style that was widespread during Woodward's (and Bernstein's) rise to fame during Watergate. The fact is that books are not now and never have been the appropriate venue for Breaking News. The publishing cycle, even for cynically churned-out crap like the Cohen/Bolton books, simply takes too long. Any information you collect is coming out in six to eight months at best, more likely a year-plus.
Woodward certainly is a person who has access to newspapers; WaPo or the Times or literally any newspaper that isn't a far-right tabloid would have taken this story at the time he learned about it. The problem runs deeper than Woodward and these tapes, though (which given what we have experienced with Trump for four years, may not have made the enormous difference you think). There simply isn't much investigative journalism happening anymore, the kind that kept people glued to newspapers Back in the Day. We are now similarly glued to the internet, but it is a substitute and not a replacement. The economic model of news delivery online provides very little space for stories that take a long time to develop and break. Investigative journalism hasn't disappeared entirely. There is, however, a lot less of it than there used to be. And less of it than we need.