That's actually a good point. If the US government issues a National Security Letter or uses the All Writs Act to force Google to distribute a backdoored version of an app to a target of a criminal investigation, then it might be an open and shut case of compelled speech (challenged under the First Amendment, assuming the target had standing), but it's not obvious that actions done by a private company to fulfil a legal obligation from the government can ever be prosecuted as fraud.
It might be helpful to consider a simpler situation, where an FBI agent pretends to have a shipment of drugs which a drug dealer attempts to buy. If the dealer hands over money and doesn't receive the drugs, my non-expert understanding is that they can't then sue the government for fraud, presumably because of qualified or sovereign immunity.
The reason the government won't give back the money is that it will initially be evidence, and then subject to civil asset forfeiture. I don't believe that it matters that the item being bought was illegal, as if property law doesn't apply to illegal goods, since, in theory, if one drug dealer stole drugs from another drug dealer, the government could prosecute the perpetrator for both the theft and the possession of the drugs.