Tailscale recently added local file transfers called Taildrop https://tailscale.com/kb/1106/taildrop
This really solved this issue for me, right click a file and select the receiving peer and it just appears instantly on the other device.
I would assume that limitation is because it's on the roadmap, but they want a different UI for it, or more control, or to see how beta goes with just your own devices, give some time to think about how it should work, etc.
Because they've had to specifically put that limitation in place, no way they don't realise it could be useful.
I created an automated installer to provide this functionality on KDE Plasma using Dolphin this morning to emulate the experience of sharing via TailDrop on Mac for Linux.
