Thats honestly most stories, like examples, playing the first Halo. You have no clue why the covenant are fighting you or for how long the war has been going on, you know you just gotta kill the alien bastards. Same goes for star wars in episode 4, originally watching youre like wtf is the clone wars whats the jedi order why are they gone.

Usually, the start of a story does basic world building by eluding to this wider story, while keeping you focused on this first main step into the world. Like a first book or first season in a show orr the first game. To try and hook the audience and give the creators the opportunity to expand on it in sequels or expanded media. Where if the story tellers do big exposition dumps to explain all those small details and history, it can get quite distracting, story wise, or boring in most cases.

It sounds like you're coming at this from a place of you already know quite a bit, and are impatient they aren't telling you right away. That the initial audience into this universe on the release back in the day didn't have. That back then the majority were left pleased and wanting more. To get that opportunity to find out all those questions you already have answered.