They have to be hedging their bets on this getting renewed either within Amazon if they fix the licensing issues or elsewhere. The whole build up of the Cara and Xan storyline at the start of each episode which even with the best will in the world can't be resolved in the final episode.
While i'm certain we'll get a decent conclusion to the Inaros arc, there is so much protomolecule related stuff in the final 3 books that hasn't even had the surface scratched yet. Don't worry, i'm not going to post anything about the final books.
Also this final season is really hurting without Alex on the crew, he was a big part of the heart of this show and his absence is really noticed.