Never. The reason MINIX 3 didn't dominate the world has to do with one mistake I made about 1992. At that time I thought BSD was going to take over the world. It was a mature and stable system. I didn't see any point in competing with it, so I focused MINIX on education. Four of the BSD guys had just formed a company to sell BSD commercially. They even had a nice phone number: 1-800-ITS-UNIX. That phone number did them and me in. AT&T sued them over the phone number and the lawsuit took 3 years to settle. That was precisely the period Linux was launched and BSD was frozen due to the lawsuit. By the time it was settled, Linux had taken off. My mistake was not to realize the lawsuit would take so long and cripple BSD. If AT&T had not brought suit (or better yet, bought BSDI), Linux would never have become popular at all and BSD would dominate the world.
Now as we are starting to go commercial, we are realizing the value of the BSD license. Many companies refuse to make major investments in modifying Linux to suit their needs if they have to give the code to their competitors. We think that the BSD license alone will be a great help to us, as well as the small size, reliability, and modularity.
My first UNIX experience was in the 1984-85 timeframe and my first job out of college was developing software for intelligent I/O controllers for a UNIX System V mini-computer. I remember what commercial UNIX was like in those days. You may have wanted it but the options were limited and expensive. On the 80286, you had XENIX. When the i386 came out, there were a number of nice options including Interactive 386/ix and even SCO UNIX. Yes SCO had a decent product back in the day.
When I could finally afford a computer capable of running some UNIX-ish system, I found myself in on the consumer side of what the question is about.
Why did I choose a Linux distribution over a BSD? I honestly don't remember. My vaguest recollection is that I preferred System V more than BSD systems and Linux leaned to System V. I doubt this was a factor for most others though. If I had to guess, I would go back and look at how you had to obtain it, community responses to newbies, etc.. Was the AT&T lawsuit have factor? Maybe. Linux was certainly perceived to be immune from that lawsuit among those I knew. It did not suffer from that heritage.
Finally, I want to look back with the free software community building experience I have. When viewed from this perspective and the prism of time, I think the answer has a lot to do with what we should have learned from Google Summer of Code. A project has to be easy to obtain, get started with, contribute to, have a vibrant and friendly community, etc.. The license is important but as long as it is imposes legal impediments or obligations, that won't stop most people. In the old days, Minix was not really easy to obtain and was not focused on general use. It was not available as an impulse download. That was enough of a hurdle to stop a lot of folks.
When one examines the choices faced by someone who wanted a UNIX-like system on their personal computer in the early 1990's, it is easy to see how Linux was the default choice. It simply did not have the "targeted to teaching operating systems" stigma, was easy to obtain, and didn't have a lawsuit looming over its head.
But one of the nice things about free software is that if there is interest, a project will continue on. MINIX 3 is a great OS that has a BSD-style license, is easy to obtain, and they are clearly interested in MINIX 3 being used for more than teaching operating systems design. Variety is the spice of life. I would recommend that you give it a try and tell them I sent you.