tldr: chapo.chat isn't ready yet.
Don't worry, you'll get to be called libs by the users from lemmygrad.ml Soon™.
[chapo.chat is] running a heavily modified version of lemmy forked months ago, for not just the front end, but the back end as well. Once they’re up to date with the most recent lemmy versions that have federation working, then we can try federation, on the back end at least. Their back end devs are great, but their front end devs contribute nothing upstream, and will have to re-create all the federation-related parts of the lemmy-ui code for their own fork.
EDIT: See @Beatnik's comment
Because the data probably isn’t compatible with both front ends after federation was implemented. Chapo chat needs to add some new ui features to be able to see linked instances, what instance a post or community belongs to, and so on for the site to really be usable. That’s my guess.