This is more or less baked into the SSH protocol because the exec request only has a single string for the command line.

Also the reason echoing a MOTD from rc files or similar crap breaks tools like rsync or scp which use SSH as a neutral transport. SFTP isn’t affected because, while using the three-pipe as a transport, it’s a separate subsystem with its own SSH request type to initiate the channel (just like X11 or port forwarding).

If you control client and server you can define your own subsystems and invoke them directly, which avoids this whole mess.