Only thing i don’t realy get is what the point of having it divided in different service is

You can think of them like different email clients. Sure, different email clients all send and receive the same messages via IMAP / POP / SMTP, but they offer different user experiences. Some users might prefer Thunderbird, others Outlook, etc.

Same thing with Lemmy, kbin, and Mastodon. They all post content via ActivityPub, but some users might prefer the microblogging experience of Mastodon, or the UI of Lemmy or Kbin. I am sure other projects will come along too if the Fediverse takes off that caters to other users' needs.