@delroth It's kinda on purpose, I think?
On one hand, if you accepted numbers from other instances and summed them up:
a) anyinstance could inflate any number sky-high (so _some_ instance somewhere would probably be doing such things to troll, because that doesn't seem subjectively as spammy as posts),
b) you'd need to somehow synchronize things; activitypub is already bad at synchronizing whether X follows Y between their homeservers, so this would be in practice perpetually slightly borked (that said, boosts _are_ propagated to the original instance, so propagating count changes in the other direction would in principle work).
On the other hand, this seems to be "societal engineering by lack of feature", similar to the claimed reason behind lack of quote replies in vanilla mastodon.