There's a list of features and readiness at https://btrfs.wiki.kernel.org/index.php/Status - there were people who didn't check it and used unstable features and experienced issues. This is partially on the project for not making it more explicit.
The second is that there are people who read that, see the unstable raid5/6, and are vocal about btrfs being overall broken / not ready rather than accepting that feature just not being available yet.
Here's a list of failures from zfs, including many kernel panics for example https://github.com/openzfs/zfs/labels/Type%3A%20Defect - is it broken and shouldn't have been released?
Maybe to put it differently: new file systems should offer improvements wrt reliability for stable features of the file systems of the previous generation; regressions are unacceptable.
How long are we expected to wait? It's been over a decade.
btrfs was touted as a spiritual successor to ZFS. raidz5 is a core feature of ZFS, not an incidental extra feature.
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