It's likely a human resources problem. For every competent FreeBSD or Illumos sysadmin there are 10x equally experienced with Linux. And those numbers are much worse outside of major cities. The commercial support from Ubuntu tips the scales.
I made this same decision at my last job. I ran Solaris and Illumos on our file servers and loved it, but a year before I left I ported all the pools to Ubuntu so my successor only needed to be Linux competent and ZFS trainable.
Sometimes when choosing tech it's not what's technologically superior solution nor what you personally could run well, it's what's best for your coworkers, your successor and the organization in the long term.
I made this same decision at my last job. I ran Solaris and Illumos on our file servers and loved it, but a year before I left I ported all the pools to Ubuntu so my successor only needed to be Linux competent and ZFS trainable.
Sometimes when choosing tech it's not what's technologically superior solution nor what you personally could run well, it's what's best for your coworkers, your successor and the organization in the long term.