Agreed. Government doesn't get to force a company to make their product compatible with another platform. Unless I am missing it, did the DOJ plead that Apple actively prevented Google from making Android work with Apple Watch? If so, then it would be a different story.
Couldn't Apple also make a 1st amendment argument that the government can't force them to "speak" something (make iPhone work with Android)?
The government argued that Apple does not support Apple Watch on Android, which makes it cost prohibitive for Apple Watch users to switch to Android, since they'd have to buy a new smart watch. I wish this was made up, but it's 20% of their arguments for Apple violating anti-trust law.
Some would argue that Apple is obligated to provide all the API necessary to let Google implement support for Apple Watch on Android phones because anything short of that would be an abuse of its monopoly position in the "Apple Watch host device" market.
I don't think DOJ is arguing that. Their argument seems to be that Apple isn't supporting Android. Providing an api is different from actively supporting another platform. API would usually be agnostic.
Also, couldn't Apple make a first amendment argument?
Yes, but I'm saying some would respond to your claim that it's Google's responsibility to bring Watch support to Android with the fact that Apple doesn't allow 3rd parties to bring Watch support to any platform. It's like saying it's Google's responsibility to support iMessage on Android: sure, but it's not technically possible anyhow without Apple doing work.
I agree that government forcing interoperability in this way is pretty concerning. Maybe Apple is an exception (arguable, I don't believe it, but not preposterous).
Government literally forced Microsoft to make their products interoperable in a previous antitrust case from 2001. The defendant didn't attempt a 1st Amendment argument.
Couldn't Apple also make a 1st amendment argument that the government can't force them to "speak" something (make iPhone work with Android)?