Well, now you have put your finger on it.
You will find the vast majority of PIAs, particularly with lowered interest rates (for the purposes of ensuring repayments are affordable for the debtor) are often "negotiated" down on the basis that they are proposing a variable rate to be applied in the debtors arrangement. In particular, with funds rather than banks. It is funds who primarily bought non-performing loans, and we need not explain the reasons why or how a large proportion of these loans stopped performing in the first place (read: thread title)...
Any information regarding the process leading up to and including this should be made available for the knowledge and benefit of those facing into arrangements that will allow the lender/vulture to "impose" excessively high interests rates on the debtor for the duration of the term of the mortgage on their own home. While they may now become solvent, they also may now be facing the same problems as before - presumably their RLE's have not changed, but their interest over the term may well be higher now than what brought them to insolvency in the first place. In this circumstance or under certain types of arrangements (e.g. typical arrangements with vultures), the debtor has no recourse to seek a fixed rate or seek a better rate from another lender now, or in the future. In particular, if their secured debts (e.g. their own home which "they get to keep") is subject to any write down as part of the arrangement.