unshare then overlay mount fails

I Cannot overlay mount after creating an mount namespace with unshare

$ unshare -rm# mount -t overlay overlay -o lowerdir=/bin,upperdir=/overlay/upper/bin,workdir=/overlay/work/bin/ /overlay/merged/bin/mount: /overlay/merged/bin: permission denied.

Also tried

$ unshare -rmpf --mount-proc# mount -t overlay overlay -o lowerdir=/bin,upperdir=/overlay/upper/bin,workdir=/overlay/work/bin/ /overlay/merged/bin/mount: /overlay/merged/bin: permission denied.

Is this a limitation of wsl or because I'm not really root or am I missing something?

bind mount works

# mount --bind /bin /overlay/merged/bin/# grep bin /proc/self/mountinfo127 126 0:19 / /proc/sys/fs/binfmt_misc rw,relatime - binfmt_misc binfmt_misc rw137 106 8:16 /bin /overlay/merged/bin rw,relatime - ext4 /dev/sdb rw,discard,errors=remount-ro,data=ordered