Why manga ending is so unsatisfying

Well, I really like Blame, so I was glad to read another work of this author, and it had his awesome sci-fi style.

But ending is really bad. But not bad overall, author made it bad. If whole story was going showing Gauna as mystic force without any clues, then ok, but author seeded references to future large plot twist the whole way.

1) History says that first Gauna ever encountered had human shape (???) 2) That scientist talking about why Gauna copies imperfect human body like he knows something? (After ending, why, really?) 3) There and here heroes say that may be Gauna is not neccessary enemy, that people and Gauna just can't communicate 4) That ancient abandoned ship containing spears

And other less obvious stuff. So each chapter near the ending I was like: yeah, this one will blow it. And oops, manga ended. Nothing explained. What is Gauna, is it artificial or natural, is it kind of life or something different, where did it come from, what it seeks, does it have consciousness. NOTHING.

But they just blew up large one and that's it? Nice. Why when author bothered to put this details in first place?