Is it the lack of drivers? Better availability of other 3rd party software for Linux? The package manager? Or just "more brains in Linux"/"our CTO grew up with Linux"?
Edit: this is a legitimate question. I know previously Linux-related ZFS efforts used FUSE, but ZoL is native. I assume performance should be roughly equivalent between Linux and FreeBSD, certainly.
Also, experience tells me that illumos and FreeBSD based systems will always perform faster than Linux with regads to ZFS but I'd have to publish a full line of benchmarks and I bet even those would get vehemently disputed because Linux is all the rage right now, so that's a lost cause: you have to try it for yourself and make up your own mind.
Setting this aside, all usage hours are not equal. How do you compare an hour of enduser desktop usage on Ubuntu 23.57.something to a usage hour of a commercial NAS storage solution internally based on FreeBSD and ZFS? Do you think the enduser performed comparable product testing cycles?
I've seen ZOL systems where the zpool claimed it was online, but contained no vdevs. `zfs list` had no datasets, but datasets where mounted and trying to read from them got your process stuck in-kernel. It just lost/forgot its devices.
Up until one of the latest releases on every boot you could roll the dice by which name your pool would import the devices. Behaving differently on identical machines and setups. Personally, I am still not trusting that problem to not reappear again.
ZOL is bolted on. With a large nailgun. Simple as that. At times, it feels about as integrated as pjd's original patches distributed on the FreeBSD mailinglists. And since this division is not technical, but legal, based on the license choice made 30 something years ago for Linux with regards to where the code could be exported to and what could be imported into, this situation will not resolve itself.
zpool upgrade -v; zfs upgrade -v