miriamrobern@dice.camp the reason is two-fold:
There is no standardized way to communicate "mutuals" as a group between instances. Comparatively, there is one for "public".
You cannot easily tell whether your mutuals are the same as another server's list of mutuals, so there's a reliability guarantee that is hard to satisfy.
These are solvable problems, but sadly it isn't as low hanging as it initially seems 😅