ZFS managing its own cache that sidesteps the existing pagecache infrastructure and requires dedicating more memory for it to function well than you otherwise would with any other filesystem.

ZFS sidestepping conventional device and mount handling with the way it "imports"/"exports" ZFS pools, usually auto-mounting all datasets straight to your system root by default - if you have a dataset named "tank", it automounts to "/tank".

ZFS operation itself being an inexact science of thousands of per-dataset flags and tunables (again not set through the common path with mount flags), and unless you run something like TrueNAS that sets them for you it's probably best to pretend it's not there.

Common configuration with decent performance commonly involving complexities like L2ARC.

It's far too invasive and resource consuming for a general purpose machine, and does not provide notable benefit there. A dedicated file server won't care about the invasiveness and will benefit from the extra controls.

btrfs fell short by still not having its striped RAID game under control, only being "production grade" on single disks and mirrors for the longest time - probably still?