The net worth of the company is their assets minus their liabilities and that represents the value that the company has if they paid off all their liabilities.
Management of these companies has, over time, caused the value of assets it has acquired to decrease so much that the cumulative value destroyed exceeds the value of all their assets currently.
Their pay and assets will not appear to fall in numeric terms as inflation pushes up the value of all the things they need to buy, whilst pegging their income and assetsvalue to a never rising floor.