There are a variety of cases that the Government declines to intervene in and which should likely not be pursued by the relator. For example, if the company has no financial assets or has many debts, you could win your case--but no money. Second, the Government agency involved may strenuously oppose the claims and may even testify in favor of the defendant. Such cases could be disastrous for the whistleblower.

Frequently, cases involve several million dollars of damages, but may require hundreds of thousands of dollars in expert witness fees, document copying expenses, or extensive motion practice, making them difficult to pursue efficiently and economically.  Health care cases could involve patient confidentiality issues, for example, making litigation quite complex. 

Some cases may simply be without merit or there are not enough facts available to prove the claims, even though there was enough of a basis to file an action.