I feel a lot of laws dictate what private companies provide us. For example a butcher's meat cannot be covered in rat poison. A hyperbolic example but for giant chat services like this where the wield an incredible amount of power because of scale they are still subject to restrictions by the government for the benefit of the people. The government totally has that overriding right because your companies operating in there county. Don't like it the same way the user has no choice but to not use your interface the company has the right now to operate in the country. Personally I think the api format is a little ambiguous but it's incredibly naive to think that companies cannot be subjected to laws on how they do business just because they built a computer service. With adoption comes regulation to protect both users and companies

The same principle behind antitrust laws: dismantling monopolies is good for the public and good for innovation

Lacking an open-for-all-comers API is not in fact an antitrust violation.

I agree of course, it's not a violation of any laws. I just thought you were asking for some moral principle to justify pressing a developer to make an API available

I mean, it's just not antitrust, at all. A vendor is not coherently a "monopoly for their own products".

As the world changes, we can't always expect new behaviors to ideally fit existing moral principles.

Is there a moral principle preventing a power company from providing you with all your electrical appliances and forbidding you from using those not provided by them?