How do you know this?
Now, try to apply that same reasoning to your allegation without looking silly. Yes, the USG has secretly run certain aspects of a public biowarfare program - and when it came to light they paid. Boom, they couldn't keep it secret and they couldn't escape the consequences (lots of very damaging legal cases and hearings). Finally, do they have an incentive? No - as I said, it makes no sense for them to reduce the cost of yet another world ending weapon. Now you could point to Russia getting caught with massive stockpiles of Anthrax after they claimed to end the program... but their nuclear program's credibility isn't comparable - they've always demonstrated clear signs of insecurity about it. That isn't the case for the USG.