I remember this coming up in a blog post by the creator of Shellcheck a while back [0] and being discussed here [1].
One reason given is this:
> Assuming the OSS projects aren't a conflict of interest
Apple is so secretive even internally that you can never guarantee whatever you're working on in your free time does not conflict what someone at Apple is working on secretly.
One reason given is this:
> Assuming the OSS projects aren't a conflict of interest
Apple is so secretive even internally that you can never guarantee whatever you're working on in your free time does not conflict what someone at Apple is working on secretly.
[0]: https://www.vidarholen.net/contents/blog/?p=859
[1]: https://news.ycombinator.com/item?id=22279585