It's about the drivers. Getting traction with a new OS is all about driver support. Which is what makes launching a new OS hard, assuming your goal is to be popular. You have to inspire an army of driver writers.
I don't think it helped that the BSD distributions were very opinionated about their userlands, where in Linux you had lots of choice.
In hindsight, it seems to me the BSD guys simply blew their shot by infighting at a time when early adopters were clamouring for a Unix like, and didn't care about the BSD purity war.
That was where the snowball started. Linux had no real advantage other than the cooperative nature of the community.
But it seems plausible that someone, somehow, managing to get one important driver into Linux that was missing from BSD might have helped to get the ball rolling, enabling "Linux has better driver support" to become a self-fulfilling prophecy, encouraging driver writers to write drivers for Linux (rather than BSD) and for Linux to include them. Presumably BSD eventually largely caught up, but by then the race had already been lost.
For me personally it was the Panasonic/Mitsumi interface CD-Rom on the Sound Blaster cards. Vague and possibly incorrect memory suggests 386BSD (and maybe FreeBSD/NetBSD) you could get an expensive SCSI cd-rom working, but not the Panasonic/Mitsumi ones that were vastly cheaper and more available.
Because the internet simply wasn't available in a form useful for downloading a distribution, CD-Roms were the only practical way to install a Unix-like. Cover discs, or Slackware, or Yggdrasil were available at your local book store.
The MPC[0] standard was kind of on it's knees during that period, so it was pretty hard to keep up with the variety of hardware on desks at the time.
This old usenet post from 1992 [1] has contemporary reports from where 386BSD was competitive, but the general consensus even then was "Linux works on more affordable hardware" so the problem must have existed before that post.
edit: [2] This salon article seems to point the finger at the Jolitz's approach to development.
[0]https://en.wikipedia.org/wiki/Multimedia_PC#:~:text=The%20Mu...).
[1]https://www.linux.co.cr/free-unix-os/review/1992/1102.html
I'd been collecting old BSD stuff from the era, and even 4.3BSD/Mach is so weird as well, although Tahoe i386 was doomed for not having source available. A larger issue with the platform as it wasn't open and code wasn't contributed back.