[appleflaxen]

Apple seems like a good example of where someone made a proprietary fork of a non-left license, and made only trivial contributions back.

[gsnedders]

NeXT's usage of BSD predates BSD being available under any open source license, and as such macOS/iOS's use of it seems like a direct consequence of that rather than it being under a non-left license.

[appleflaxen]

I don't understand why the license at the time is relevant. The point is that if it had been copyleft, they would be required to contribute back.

It wasn't, so they weren't and didn't.