uid=N is not very user-friendly. Normally people want to specify the name of the user, which is supported by force-user.
I'm not sure this is the answer. For other filesystems like vfat, the uid mount option is automatically resolved from a name to a number by the mount command. Maybe when it runs a separate helper like mount.fuse, the mount options are passed directly and the user name is not looked up, but I don't know.
Though I also wonder if the FUSE manpage is written incorrectly and uid=sourcejedi works as a mount option, but it wouldn't work if you run the bindfs command directly with -o uid=sourcejedi.
mount,mount.fuse,bindfs, ... ? – sourcejedi Oct 25 '18 at 14:37