I'm always surprised how often ZFS is recommended when this comes up but not BTRFS which also has checksumming and scrubs and doesn't suffer some of ZFS's drawbacks of complexity and OS integration.

This is a fair point. I think that the instability of early releases of BTRFS and the (lack of) commitment of especially RedHat made me not spend too much time working with it. The lack of a RAID solution made it not feasible for my purposes for a long time, and I was already quite familiar with ZFS through working with Solaris and FreeBSD. Trust in filesystems is hard won and easily lost[0].

I also think the popularity of FreeNAS especially contributed to the popularity of ZFS.

[0] I still look at XFS skeptically after a crash I suffered nearly 20 years ago. It’s not a rational fear, but it’s still there.