Opportunity and history (2):
If 386BSD had been available when I started on Linux, Linux would probably never had happened. - Linus Torvalds.
Berkeley Software Distribution predates Linux by almost 15 years (circa 1977). To make a long story short (and simple), the story of BSD is the story of UNIX breaking free (more than once, up to 4.4BSD Lite) of AT&T's source code and licensing. It is also about the development history of networking i.e. NET/2 and, as times changed, and academia IT overflowed to enthusiasts as communication expanded, is related to this desire of bringing this rich tradition to low cost machines i.e. PCs (one should never forget that none of that historical UNIX was made to run on the PC/386 architecture initially). But the pressure was too great for the 386BSD project to withstand its own success so to speak. The breakup which ensued (386BSD based vs. NET/2 + Mrs/Mr Jolitz 6 files) and the different focuses (386 vs. multi-platform network) basically explain the differences between FreeBSD and NetBSD (or OpenBSD). But it is all BSD, unencumbered 4.4BSDLite has trickled down to all "forks", the licensing is settled and Berkeley's amazing legacy lives on free now...
Linux/GNU is a UNIX-like OS but has no direct ancestry in UNIX. It is a product of its time (1991, much later than historical BSD) and designed to run on modern consumer hardware as well as other architectures. The Linux kernel was (and still is - for instance there were on average 9 accepted changes per hour into the 3.10 kernel) a powerful catalyst, and rapidly converting to using the GPL licensing scheme made both it and the GNU project a "perfect" fit for one another. Similar to how UNIX historical shell utilities and commands had emerged from AT&T's hold gradually up to 4.4BSDLite and NET/2, so did they through GNU which Linux enabled. Beyond the quality of the project and the leveraging of a worldwide community, an argument can also be made where Linux/GNU is seen as the most POSIX compliant free OS around and as the standard might have favored System V behavior over BSD, it is possible this also added to the attraction power of Linux.
You fork for a reason. It seems conditions existed for it to happen with BSD. It seems there is no such rationale for doing that with Linux for the time being...
