In fairness part of it was probably down to the amiable but terminally incompetent David Moores being chairman at the time. However, the main charge against Parry is that he was a commercial failure on whose watch LFC fell hopelessly behind in commercial terms, which in turn meant falling behind in footballing terms, as other clubs - notably the Mancs unfortunately - raced ahead on the financial side and consequently on the footballing side as well. He had previously done well as CEO of the Premier League, but that was more of a bureaucratic job than a truly commercial one, as the Prem didn't/doesn't have to face competition and can more or less dictate terms to anyone wanting to do business with it.
Parry's crowning glory of course was to usher in the reign of the two cowboys, telling us fans to trust him and Moores on the issue. 'Nuff said really.