We always see a Scratch Design Studio on the front page, but the Scratch Design Studio account is a Scratcher, not a Scratch Team account.

We don't know yet.

It's run by the Scratch Team and other users, and one of the managers is a Scratch Team member.

While I don't know the exact reason, one theory is that the account doesn't actually need moderator perms to do its job.

that explains why i saw a game about shooting among us in the SDS!
(no really pls scratch moderate the SDS i saw that the scratch cat had an actual gun)

It's just an account to look “official” as the studio host of the SDS with the username @ScratchDesignStudio, instead of say one of the Curators being the host. The account is only used nowadays to create a new SDS.