> If you develop APIs that requires feedback and testing, what forces you to keep it secret instead of making it public and clearly marking it as beta / experimental?

The fact that you want feedback from only people you trust.

> There is no benefit to the world in me just cloning Zoom > > There is no benefit in preventing you from using these API.

Yes there is. If the APIs are not ready, then developers cannot rely on them.

Making them available has costs, regardless of how they are labeled.

> What if you clone Zoom, with a better business model and/or making it open source?

You can do that just as well once the APIs are public.

> Or if you create a product that finds an unforeseen application to these new APIs? Your feedback is valuable too.

It’s possible that there is some unforeseen feedback from a random person that is valuable, but given that most people have no incentive to give good feedback, most of the feedback will likely be garbage.

This is why they partner with people who have proven experience.