There are a few obvious, systemic reasons for this. The power imbalance between a publisher and all but a handful (like four or five) of individual authors; the difference between a collection letter from an author for something that can be jimmied through creative accounting and a collection letter from the landlord for the rent; the general disdain for authors prevalent in the higher reaches of publishers; and, perhaps most interestingly, the Bankruptcy Code, which puts authors and other licensors of intellectual property pretty close to the bottom of the heap when extracting money from a bankrupt debtor. Perhaps the Bankruptcy Code should be revised to give a higher priority, or even a superpriority, to licensors of intellectual property; perhaps not; perhaps it just requires a two-by-four upside the head of management in the publishing industry. Or, perhaps, it's an insoluble problem.
In any event, I'm not surprised. Were I the plaintiff's lawyer, I would also demand that an outside accountant examine not just the books of account, but the source documents and contracts, when determining the amount of royalties due. But that's me. And I'm not the plaintiff's lawyer.