You could say that Linux is AT&T's fault
Recently on Twitter, I gave in to temptation. It went like this:
@tux0r: Linux is duplicate work (ref.: BSD) and they still don't stop making new ones. :(
@oclsc: But their license isn't restrictive enough to be free! We HAVE to build our own wheel!
@thatcks: I believe you can direct your ire here to AT&T, given the origins and early history of Linux. (Or I suppose you could criticize the x86 BSDs.)
My tweet deserves some elaboration (and it turns out to be a bit exaggerated because I mis-remembered the timing a bit).
If you're looking at how we have multiple free Unixes today, with some descended from 4.x BSD and one written from scratch, it's tempting and easy to say that the people who created Linux should have redirected their efforts to helping develop the 4.x BSDs. Setting aside the licensing issues, this view is ahistorical, because Linux was pretty much there first. If you want to argue that someone was duplicating work, you have a decent claim that it's the BSDs who should have thrown their development effort in with Linux instead of vice versa. And beyond that, there's a decent case to be made that Linux's rise is ultimately AT&T's fault.
The short version of the history is that at the start of the 1990s, it became clear that you could make x86 PCs into acceptable inexpensive Unix machines. However, you needed a Unix OS in order to make this work, and there was no good inexpensive (or free) option in 1991. So, famously, Linus Torvalds wrote his own Unix kernel in mid 1991. This predated the initial releases of 386BSD, which came in 1992. Since 386BSD came from the 4.3BSD Net/2 release it's likely that it was more functional than the initial versions of Linux. If things had proceeded unimpeded, perhaps it would have taken the lead from Linux and became the clear winner.
Unfortunately this is where AT&T comes in. At the same time as 386BSD was coming out, BSDI, a commercial company, was selling their own Unix derived from 4.3BSD Net/2 without having a license from AT&T (on the grounds that Net/2 didn't contain any code with AT&T copyrights). BSDI was in fact being somewhat cheeky about it; their 1-800 sales number was '1-800-ITS-UNIX', for example. So AT&T sued them, later extending the lawsuit to UCB itself over the distribution of Net/2. Since the lawsuit alleged that 4.3BSD Net/2 contained AT&T proprietary code, it cast an obvious cloud over everything derived from Net/2, 386BSD included.
The lawsuit was famous (and infamous) in the Unix community at the time, and there was real uncertainty over how it would be resolved for several crucial years. The Wikipedia page is careful to note that 386BSD was never a party to the lawsuit, but I'm pretty sure this was only because AT&T didn't feel the need to drag them in. Had AT&T won, I have no doubt that there would have been some cease & desist letters going to 386BSD and that would have been that.
(While Dr Dobb's Journal published 386BSD Release 1.0 in 1994, they did so after the lawsuit was settled.)
I don't know for sure if the AT&T lawsuit deterred people from working on 386BSD and tilted them toward working on Linux (and putting together various early distributions). There were a number of things going on at the time beyond the lawsuit, including politics in 386BSD itself (see eg the FreeBSD early history). Perhaps 386BSD would have lost out to Linux even without the shadow of the lawsuit looming over it, simply because it was just enough behind Linux's development and excitement. But I do think that you can say AT&T caused Linux and have a decent case.
(AT&T didn't literally cause Linux to be written, because the lawsuit was only filed in 1992, after Torvalds had written the first version of his kernel. You can imagine what-if scenarios about an earlier release of Net/2, but given the very early history of Linux I'm not sure it would have made much of a difference.)