For what it’s worth I generally agree with you, and especially think the people who treat /all as their own personal feed are nuts, but nonetheless it’s something that some people do 🫠

Everyone has their own preferences about how to use things!

Browsing the global/all feed is one way to find new communities, and some people just like using it in general rather than defaulting to a subs-only view.

Just be aware that some places/connections have trouble connecting with it: https://catbox.moe/faq.php (under Connectivity Issues)