Apple (re)started on the base of a free and OpenSource BSD system.
macOS is not a BSD. It does have some BSD components, but their importance is vastly overstated. Its kernel is not a BSD-like kernel. Its UI isn't X11. Many of its command-line tools aren't BSD.
They build macOS on top of free standards like OpenGL.
OpenGL is deprecated in macOS.
LLVM had major success (OpenSource) and lot of other OSS stuff founded the success of Apple (you name it).
Much of LLVM's success is due to Apple's heavy investment in it. It's a two-way street.
Microsoft based it's success with Azure on OpenSource tools (where would Azure be without BSD?).
Azure is largely Windows and Linux, neither of which uses much BSD at all, so… uh… probably in the same place?