Well, for one, it's a giant crap on the fans because it's a series finale without, you know, finalizing things. Then it could be a double crap on the fans if Bezos isn't tempted. Which, based on the low quality of the end, I wouldn't, if I were him.
I'm a fan. I'm a huge fan.
I don't particularly feel crapped on.
I know for a fact because of the books that the story of The Expanse is, pardon the pun, so much more
expansive than even another 15 episodes of this show can cover.
It ended the major arc of the past two seasons (the Belter War) and it left it open-ended for the casual viewer to possibly want to explore the rest in the books. In the meantime, those of us paying attention (you know, the fans) know that showrunners are exploring as many avenues as they can to continue the story told in the show (since it has veered slightly from the books), including movies, animation and maybe even comics.
Maybe YOU feel crapped on, but you don't really approach most shows as a fan. You approach them as someone who has a taste and THEY have to conform to YOUR tastes or YOU aren't happy.