I guess you can argue that WebKit, CUPS, Darwin, LLVM etc were open-source before Apple started using/sponsoring them (or based new software on them) and so had to continue, but Swift was a from-scratch project that was open sourced.

As for zero-knowlege encryption, iCloud Keychain is although the rest isn’t, you’re right there. Hopefully they’ll move in that direction.

I'm not saying that Apple is staunchly against FOSS or anything, and they absolutely do release a lot of FOSS stuff (which is awesome!), but their platform is absolutely not FOSS. I still can't compile my own iOS or MacOS.

If Apple open-sourced their OS you'd have a CentOS in half a day. Apple definitely doesn't want clones, it means less customers and less cohesive branding, so is there any reason this wouldn't be a very damaging move?

It's definitely possible that this would have detrimental effects to their bottom line. I know I would start buying their products, and I would encourage others to do so, though, I'm not sure if that would make up for the loss.

But that's irrelevant to the point. The point is that Apple prevents users from understanding or controlling how the user's data is being used. Just because we understand why they won't fix it doesn't make it any less true that they could fix it, but choose not to.

And that's what I mean by "putting their money where their mouth is". They talk a big talk about protecting their users, but their actions are different than their speech.