Obviously this was not FSF's intention and there's the affero GPL licence which deals with this shortcoming.
If both companies were legally bound to release all their modifications then FreeBSD would move forward faster and Juniper and Cisco would have to compete on other strengths than 'the secret sauce'.
You have to ask yourself why if -'BSD is so much better for companies' as BSD advocates state, Linux is enjoying so much more company support in the form of developers and code?
Those who are totally delirious try to blame a lawsuit 20 years ago where all mindshare went to Linux. That's nonsense, if the BSD were so much better equipped to handle the needs of companies then it would have gained on Linux during these 20 years, not slowly faded into near oblivion.
As it has turned out companies (particularly proprietary) LOVE picking up BSD/MIT licenced code, but they are (quelle suprise!) nowhere as willing to submit code under BSD/MIT.
Meanwhile companies are much more willing to submit code under GPL conditions, which has lead to Linux incredible rise as the largest open source collaboration in the world.
If they keep their enhancements internal then again it's out of the scope of the GPL, but it also severely limits their use of said code.
Ofc, if you use closed bricks stone house with patented design of unknown origin, you house is gonna fall underground, unless your provider maintains and fixes it for you at certain high (due to proprietary design and resulting incompatibility) rates.
But because the ground construction is very open too, some gardens (like Red Hood etc) offer private locations, where the ground is fixed for periods of up to 10 years. Ofc at acceptable maintaining rate... but at least regular soil inspections are included in price.
Or... there are some free stable grounds of kingdom Debian and in Africa district LTS, many build their houses there, but the local folks ask for nothing and exactly that much they promise,... but it works!
As for the question of a unified BSD, these sort of suggestions always sound perfectly reasonable at first glance, until you actually look at the reasons why they aren't one project to begin with.
It has to do with endgoals, technological choices, and even ideology at times.
Also when people point at Linux and saying it's not fragmented it's mainly true, but FreeBSD is no more fragmented, nor are OpenBSD or NetBSD or DragonflyBSD.
These are all _different_ projects. they may share some code and even part of their names but again they are _different_ projects with all that this entails.
KDE,GNOME,XFCE,*Box,*WM - GTK,QT etc etc... heck you can take it as far as WINDOWS/OSX/LINUX/BSD/HAIKU/REACTOS etc
All projects which are in the same problem domain and again at a cursory glance would seem ripe for 'consolidation', but as soon as you look at the projects in any kind of detail you will see how there are reasons for why they are separate and why their respective developers have no interest in the other projects.
XorEaxEax, I want to know. Do you write code or do you just freeload on what others have done?
In general GPL does it quite inconvenient or hard for most business models to exist without releasing source. This includes embedded, general purpose OSes (servers, desktops, etc) and so on. And Linux has seriously outperformed BSD-based competitors on these markets.
You see, BSDs are 10 years older. So they had all chances to win. However, corporations behind them preferred not to disclose their improvements. Single company wins. Everyone else loses. Upstream project as whole getting stuck without resources and improvements. Then competitor appears and outruns it, using collaboration of members to improve it's development speed. So Linux does not faces lack of resources. If someone improves something and distributes it, they have to publish source as well. There are ways to workaround but risky, costly and dubious. And it would certainly make you unwelcome for kernel developers to say the least (do you remember "f...k you, Nvidia"?:)). So you will be on your own, not a part of process. This implies seriously increased development cost and so on.
In short, GPL makes it very inconvenient to be parasite and far more convenient to be part of process. BSD license does not cares so at the end of day BSD systems are getting eaten by parasites who takes the code and never returns anything.
Now we can open our eyes and figure out that:
1) Most modern SOHO routers/access points are using Linux.
2) Modern TVs and TV boxes are using Linux.
3) Android bases on Linux either.
4) Small NASes, etc are running linux as well.
Because people do not have to do the whole kernel adaptation and work is split over dozen and half of entities. Who could be competitors otherwise. But they all need good working kernel for their OS to be able to just start their competition. This serves as point for collaboration on topic. And it works.