What's up with many Fediverse services not having a public timeline?

Now that i'm getting used to being in Fedi long term i've started looking beyond Mastodon and Lemmy to the other services. And now i've started to see that some of the services, like Pixelfed, Friendica and others don't seem to have a public timeline. Seems specially absurd for Pixelfed since you WANT your photos to be visible to everybody but haven't found any instance yet that does it (maybe i'm unlucky, dunno). Is there a reason why this happens? Seems counterproductive for people who might or might not want to join the given server, you want to know what you're getting into.