>  the US gov can't legally force the companies to decrypt what they can't decrypt.

No, but they can compel the companies to disable their encryption. And in the latest 'wide net' sorts of court orders disable it for many more people than just a 'few.'

As with most things, once a business starts arguing with the government about what they can and cannot do, it is going to be very expensive for the business. Potentially disastrously so.