I think that's probably something they will wish they had done with the wisdom of hindsight, but obviously when RW wrote TSP she had no idea it was going to be so successful, and that it would bring in so much money and fame. So I'm not surprised it's not in TSP.
Apart from anything else, it wouldn't have been bought if the narrative was 'We went on the run from our debts, after losing our house because I'd embezzled a big sum from my employer and defaulted on the loan I used to repay him and shut him up, but hey, we found nature and serenity on the SWCP, so that's fine, right?'
And by the time they knew it was a bestseller, it was too late.
However, after the huge success of TSP when money was rolling in merrily and Michael Joseph clearly gave her another book contract, probably for two further books -- that's when someone thinking more clearly would have thought about ways of trying to winkle in a sanitised version of the truth, presented in the most self-excusing light ('I made mistakes, we were desperate, I couldn't bring myself to tell the full truth in TSP') and being able to say they had obviously paid back everyone to whom they'd owed money in full, and made a whacking great donation to a homeless charity. It might have worked, to an extent.
(But that's obviously only dealing with the financial side. If Moth was never ill, or had an entirely different illness, or was in fact a crack addict or something rather than someone living with CBD, hard to see how the best retro-PR could possibly have prevented that from sounding monstrous.)