If you really study macOS, and before that NeXTSTEP/OPENSTEP, you will see that it's not entirely BSD, and they didn't steal anything. NeXTSTEP was introduced in 1988s. And if you weren't hiding under a rock (or maybe you weren't born then?), you'd know that the first web browser and app store were created on NeXTSTEP. Plus, if you want to talk about Linux, Apple was a big supporter of Linux, and released MkLinux in 1996. I used to run it on my PowerMac 6100. It was sponsored by Apple Computer and OSF Research Institute.
They took parts of FreeBSD, NetBSD, and Mach/BSD, since it runs on the Mach kernel. Windows NT and SUN Solaris also use BSD code.
The BSD License allows proprietary use and allows the software released under the license to be incorporated into proprietary products. So how did they steal anything? The parts they did use, they released as Darwin, which is open source, and is composed of code developed by Apple, as well as code derived from NeXTSTEP, BSD, and other free software projects.
So where's the problem? They followed the BSD License, and give credit. You can see it when you boot macOS in verbose mode. And they released their modified code as open source. This includes things like WebKit.