Can't see many (most?) communities on other Lemmy instances via aussie.zone

Hi, why can I only see some communities on other servers?

For example, https://aussie.zone/c/technology@midwest.social works but https://aussie.zone/c/cats@midwest.social doesn't work ("404: couldnt_find_community").

I'm a Lemmy noob, sorry if I'm missing something obvious.

EDIT: The missing communities are also not visible via Community Search with All selected.